Structural studies of oriented carbon nanotubes in alumina channels using high energy X-ray diffraction

Structural studies of multi-wall carbon nanotubes prepared by template pyrolytic carbon deposition from thermal decomposition of propylene at 800 °C inside channels of an alumina membrane have been performed using X-ray diffraction. The two-dimensional diffraction pattern of the deposited carbon nanotubes, recorded directly within the alumina template using an image plate detector, exhibits two dark arcs corresponding to the (0 0 2) graphitic reflection. The anisotropic scattering distribution indicates alignment of the nanotubes. The diffracted intensity was measured for the powdered samples after removing the alumina membrane using a point detector. A maximum scattering vector of K_max = 20 Å⁻¹ yielded the radial distribution function, providing evidence that the investigated nanotubes form a distorted hexagonal network that implies the presence of five-membered rings.     

Complex thermal expansion properties of Al-containing HZSM-5 zeolite: A X-ray diffraction, neutron diffraction and thermogravimetry study

Thermal expansion of re-hydrated, Al-containing HZSM-5 was studied by different diffraction techniques, as well as, through thermogravimetry. It is concluded that the nature of the remarkable shift of thermal expansion properties, that occurs in air, between 350 °C and 400 °C, where the coefficient of thermal expansion changes from positive to negative is due to dehydration of HZSM-5 and not due to dealumination. The intrinsic thermal expansion properties of dehydrated HZSM-5 are observed in the second cycle of neutron diffraction experiments performed in vacuum (10⁻⁵ Torr). Near zero thermal expansion was observed in the temperature interval between 100 °C and 400 °C. These intrinsic thermal properties were rationalized in terms of the rigid unit mode model.     

In-situ monitoring the realkalisation process by neutron diffraction: Electroosmotic flux and portlandite formation

Even though the electroosmotic flux through hardened cementitious materials during laboratory realkalisation trials had been previously noticed, it has never been in-situ monitored, analysing at the same time the establishment of the electroosmotic flux and the microstructure changes in the surroundings of the rebar. In this paper, two series of cement pastes, cast with CEM I and CEM I substituted in a 35% by fly ash, previously carbonated at 100% CO₂, were submitted to realkalisation treatments followed on line by simultaneous acquisition of neutron diffraction data. As a result, it has been possible to confirm the electroosmosis as the driving force of carbonates towards the rebar and to determine the range of pH in the anolyte in which most of the relevant electroosmotic phenomena takes place. On the other hand, the behaviour of the main crystalline phases involved in the process has been monitored during the treatment, with the precipitation of portlandite as main result.     

Investigation by neutron diffraction of texture induced by the cooling process of zirconia refractories

New fused cast refractories with a high content of zirconia have been developed to face corrosion in glass furnaces. The controlled cooling process is responsible for thermal gradients. So, thermal mismatches appear between core and edge zones of blocks. Besides, the multiphasic nature of ZrO₂ based refractories is associated to thermal mismatches during cooling. Finally, the expansive transformation of ZrO₂ can lead to stress generation.This paper is an application of neutron diffraction to study texture generated during the cooling process of zirconia based materials. In fact, it is shown that ZrO₂ crystallographic variants have particular crystallographic texture regarding the main direction of the thermal gradient in the block. It was hypothesized that a selection of crystallographic variants could be done depending on the field stress. Tensile-compressive tests at high temperature have been done, to reproduce stress environment during the transformation of zirconia.     

Structural features in aligned poly(3-alkylthiophene) films revealed by grazing incidence X-ray diffraction

The structural ordering in as-spun and rubbed (then annealed) thin films of poly[(3-hexylmethoxy)thiophene] has been investigated by means of grazing incidence X-ray diffraction (GIXRD) and the results have been compared with the structural data as obtained from XRD on powder samples. In the structure of the as-spun films the thiophene rings in the backbone lie parallel to the plane of the interface with a well-defined separation among the chains of 19 Å. Rubbing the films creates a unique direction in which the domain size is increased, whereas ordering normal to the rubbing direction is greatly diminished, leading to dichroic behavior. Annealing the films at 95 °C seems to have no significant effect on the ordering thereafter.     

X-ray diffraction of multiwalled carbon nanotube under high pressure: Structural durability on static compression

The structural durability of multiwalled carbon nanotubes under hydrostatic and non-hydrostatic compression was examined by in situ X-ray powder diffraction at room temperature. No interlayer interaction such as sp³ hybridization that could lead to hexagonal diamond in graphite was observed under compression up to 52 GPa, even though the nanotubes were similar in compressibility to graphite. This result could be attributed to the nested structure, which makes the interlayer stacking of carbon atoms take on an irregular arrangement. Despite the history of non-hydrostatic compression, electron microscopic observation revealed that the structure remained nested tubular. This reversibility suggests the nanotubes have strong durability on non-hydrostatic compression under extreme pressures.     

Accelerated carbonation of cement pastes in situ monitored by neutron diffraction

In-situ monitoring of the changes that take place in the phase composition of cement pastes during accelerated carbonation (100% CO₂) for different binders, has been carried out, by taking Neutron Diffraction patterns in parallel with the carbonation experiments. The variation of the intensity of chosen reflections for each phase along the experiment has been used to monitor concentration changes and has supplied data, in real time, for fractional conversion of different phases (Portlandite, Ettringite and CSH gel) of the hydrated cement pastes. Fitting of these results has allowed to make a qualitative approach to the kinetics of the carbonation of the different phases and extracting conclusions on the microstructural changes that takes place during the carbonation of cement pastes.     

Investigation of the structure of ettringite by time-of-flight neutron powder diffraction techniques

The crystalline structure of ettringite, Ca₆[Al(OH)₆]₂(SO₄)₃·∼26H₂O, was investigated using high-resolution time-of-flight neutron powder diffraction techniques. The powder diffraction data were subjected to Rietveld crystal structure refinement. The resultant ettringite crystal structure confirmed the positions of Ca, Al, and S atoms while permitting a more precise determination of the locations of O and H atomic positions than in previous X-ray and neutron diffraction studies. A discussion of the ettringite hydrogen bonding network is presented, illustrating the role of hydrogen bonding in the stabilization of the ettringite structure.     

Microstructural evolution during charcoal carbonization by X-ray diffraction analysis

X-ray diffraction (XRD) of monolithic pieces of carbonized medium-density fiberboard (c-MDF) provided new insights on the microstructural evolution occurring during charcoal carbonization. Classical XRD theory was used to correlate the {002} peak intensity to the amount of carbon in large turbostratic crystallites and to bulk dimensional changes. This new analytical technique could be used to study the microstructural evolution of other monolithic carbon materials (including soft carbons) or of specific processes (including chemical activation). The quasipercolation model, a new ‘percolation-like’ model, was created based on XRD analysis of monolithic c-MDF. As the carbonization temperature (T_carb) increased above 600 °C, the large turbostratic crystallites grew very little, but the graphene sheets grew substantially. Volumetric shrinkage suggested that turbostratic crystallites were drawn closer together as the low-density disordered carbon was converted into high-density graphene sheets. At approximately 900 °C, the large graphene sheets and the large turbostratic crystallites significantly impinged on each other. The increased impingement of conductive phases with increasing carbonization temperature would cause the commonly observed nonmetal-metal transition of hard carbon materials. The quasipercolation model also suggested the source of the nanoporosity that is critical in activated carbons.     

X射线粉末衍射法鉴定无标签化学试剂

运用X射线粉末衍射法，再结合红外光谱、形貌观察等方法来对失落标签的结晶化学试剂进行鉴定，从而为其使用或合理的回收打下基础。     

Quantitative mineralogical analysis of hydraulic limes by X-ray diffraction

A combined selective dissolution/quantitative X-ray diffraction (QXRD) approach is proposed for the quantitative mineralogical phase analysis of hydraulic limes. The proposed methodology is validated by the analysis of two model mixtures. Afterwards two commercial hydraulic binders and one self-burned hydraulic quicklime were analysed. Chemical, thermal and microprobe analyses were performed to check the results. It is shown that the proposed selective dissolution/QXRD approach yields reliable quantitative mineralogical information for hydraulic limes in spite of their complex phase composition and the presence of amorphous material.     

Structural development of natural rubber during uniaxial stretching by in situ wide angle X-ray diffraction using a synchrotron radiation

Structural development of natural rubber during uniaxial stretching was examined by an in situ wide angle X-ray diffraction measurement using a synchrotron. During stretching, the amorphous part showed little change, i.e. an amorphous halo remained clear even at 500% strain. The fraction of induced crystals was very small, though a clear crystalline pattern was observed at 400% strain. Some polymer chains were oriented and crystallized, but most of the chains were not oriented at all in spite of large deformations of the specimen. Only a small amount of polymer chains contributes to the stress and hysteresis loss during elongation.     

Transformation of nano-diamonds to carbon nano-onions studied by X-ray diffraction and molecular dynamics

The transformation of ultra-dispersed diamond nanoparticles of about 50 Å in diameter into carbon nano-onions has been studied by high-energy X-ray diffraction and molecular dynamics simulations using the reactive empirical bond order potential. Structural models have been constructed for pristine nano-diamonds and nano-diamonds annealed at 1673 K, 1973 K and 2273 K. These models have been relaxed using the molecular dynamics method and the model based structure factors and the pair correlation functions are compared with the experimental data. All model relaxations and the X-ray diffraction experiments have been carried out at 300 K. Two starting models consisting of 5460 atoms with a single diamond core and an amorphous-like outer shell and for a twinned diamond core and a similar amorphous outer shell containing in total about 13,500 atoms reproduced correctly features of the experimental data. The atomic models of two intermediate and final fully graphitized structures, consisting of the same numbers of atoms and containing the series of defected icosahedral fullerenes describe satisfactorily the atomic arrangements for the samples annealed at 1673 K, 1973 K and 2273 K. The generated models of the nano-diamonds and the nano-onions are related to the previous observations by high-resolution transmission electron microscopy.     

Mixed impregnated thiosalt decomposition catalysts characterized by X-ray diffraction

We used the impregnated thiosalt decomposition method (ITD) to prepare catalysts of molybdenum sulfide promoted with cobalt in atomic ratios (r = Co/(Co + Mo)) ranging from 0.0 to 1.0. Measurements obtained by X-ray diffraction (XRD) show the presence of the MoS₂-2H phase in all mixed samples, and segregation of cobalt in two phases: Co₉S₈, forr 0.3, and CoS_1.035, for 0.3 r 0.5.     

Poly(1,4-trans-cyclohexanediyldimethylene adipate): Polymorphism and the structure of form I,using X-ray diffraction

Poly(1,4-trans-cyclohexanediyldimethylene adipate) or poly(t-CDA) crystallizes in two forms. Form I of poly(t-CDA) is analogous to the one reported for poly(t-CDS). Poly(t-CDA) has a monoclinic unit-cell of dimensions a = 6.938, b = 9.761, $\text{c = 15.97}\text{A}\text{?}$ and β = 41.4° and belongs to the $\text{P2}{}_1\text{n}$ space group. The calculated crystalline density of 1.181 g cm^?3 indicates that there is one chemical unit per fibre-repeat and two chains per unit-cell. The crystal structure of poly(t-CDA), form I was established using published structural data on related molecules for model building combined with a packing minimization procedure. The structure was confirmed by a comparison of calculated and observed structure amplitudes derived from an X-ray fibre diagram. The agreement index wR has the value of 0.153 for 31 observed diffraction data. The OCH₂(C₆H₁₀)CH₂O moiety of the polyester has the conformation t²_g(tg±t)^g?_tg (g, gauche and t, trans), while the adipate group is in the trans conformation. From II of poly(t-CDA) was identified through its distinct X-ray diffraction pattern, but its structure has not yet been established.     

X射线衍射法测定纳米氧化铝的平均晶粒尺寸

以六硼化镧粉末作为标准样品,根据衍射拟合结果分离出任意角度下的仪器宽化值。对焙烧后的氧化铝样品进行X射线衍射分析,结果表明该氧化铝样品为α晶型结构。对样品因素（晶粒细化、微观应变）引起的宽化值分别使用高斯分布法和Hall法进行拟合,计算出氧化铝样品的平均晶粒尺寸。将计算结果与谢乐公式计算出的各晶面晶粒尺寸值进行对比,表明Hall法测试平均晶粒尺寸更加准确,衍射峰晶粒细化和微观应变引起的宽化函数遵循柯西函数关系,确认该氧化铝样品的平均晶粒尺寸为155 nm。     

Time-resolved powder neutron diffraction study of the phase transformation sequence of kaolinite to mullite

Mullite formation from kaolinite was studied by means of high-temperature in situ powder neutron diffraction by heating from room temperature up to 1370 °C. Neutron diffractometry under this non-isothermal conditions is suitable for studying high-temperature reaction kinetics and to identify short-lived species which otherwise might escape detection. Data collected from dynamic techniques (neutron diffraction, DTA, TGA and constant-heating rate sintering) were consistent with data gathered in static mode (conventional X-ray diffraction and TEM). The full process occurs in successive stages: (a) kaolinite dehydroxylation yielding metakaolinite in the ∼400–650 °C temperature range, (b) nucleation of mullite in the temperature range ∼980–992 to ∼1121 °C (primary mullite) side by side with a crystalline cubic phase (Si-Al spinel) detected in the ∼983–1030 °C temperature interval; (c) growth of mullite crystals from ∼1136 °C, (d) high (or β) cristobalite crystallization at T > ∼1200 °C and (e) secondary mullite crystallization at T > ∼1300 °C. The calculated activation energy for the kaolinite dehydration was 115 kJ/mol; for the mullite nucleation was 278 kJ/mol and for the growth of mullite process was 87 kJ/mol; finally for cristobalite nucleation the calculated apparent activation energy was 481 kJ/mol.     

X-ray diffraction study of the structure of thin polyfluorene films

The molecular arrangement in thin films of poly(9,9-dioctylfluorene) and poly(9,9-dihexylfluorene) deposited on silicon substrates has been investigated with grazing incidence X-ray diffraction. In particular, the effect of the interface on the molecular orientation is highlighted. Both materials display a periodicity normal to the surface arising from stacked sheets of fluorene chains in both the crystalline and liquid crystalline phases. For the crystalline phase, a periodicity in the plane of the surface of 4.15 Å is observed corresponding to half the fluorene ring repeat distance along the backbone, consistent with interdigitating side-chains. For crystalline films deposited onto rubbed polyimide films, strong orientation effects are observed. In the liquid-crystalline phase, this strong in-plane ordering of backbones is lost. Poly(9,9-dihexylfluorene) exhibits an additional degree of ordering in the plane of the interface, which is likely to arise from hexagonal ordering of the backbone chains.     

Investigation of the residual stress in UO2-Mo composites via a neutron diffraction method

UO₂-Mo composites with a core-shell structure have been considered candidates for the thermal conductivity (TC)-enhanced UO₂ pellets and have demonstrated commercial potential for use in novel high-level safety reactors. Nevertheless, UO₂-Mo composites tend to form micro-cracks that are caused by the presence of residual stress (RS) during manufacturing. In this work, neutron diffraction measurements were employed to analyse the RS in UO₂-Mo core-shell structured composites fabricated by spark plasma sintering (SPS) for the first time. It was found that in the UO₂-Mo composites, the RS state present in the UO₂ matrix was tensile in nature. The RS in the UO₂ matrix increased with increaseing Mo content. There was a maximum value of 148 ± 15 MPa in the UO₂-10 vol% Mo composite. The micro-cracks produced in the high-Mo content composites were explained by the results of the neutron diffraction measurements. These results could provide significant guidance for the manufacturing and improvement of the operational performance of UO₂-Mo composites as next-generation fuels.     

X-ray diffraction studies of the thermal behaviour of commercial vermiculites

For the purpose of knowing the vermiculites which would have larger capability to retain contaminating substances heating commercial samples from different places have been identified and their thermal behaviour at several temperatures has been investigated by X-ray diffraction (XRD), electron microprobe, thermal analysis (TG and DTA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).The commercial vermiculites can be divided into two types: type 1 (Sta. Olalla, Piauí and Goiás) with Mg²⁺ and K⁺ (< 1) as the principal cations in the interlayer space, and type 2 (China E, China W, China G and Palabora) with K⁺ (approximately = or > 1) and/or Na⁺ and/or Ca²⁺ with or without Mg²⁺ as the principal interlayer cations.The process of dehydration in situ with the temperature seems restricted to interlamellar water monolayers of 1-WLHS type-1 of vermiculites, without dehydration to a zero-water-layer-hydration state (0-WLHS) and the dehydroxylation starts at lower temperatures than in vermiculites of type 2. The maximum hydration state exhibited by the type-2 samples at ambient temperature was equal or lower than the monolayer hydrate, the dehydration process in situ with the temperature was slower and the dehydrated vermiculite coexists with a mica-like structure.The behaviour of vermiculites at elevated temperature examined in situ can be understood considering that the vermiculites constitute a complex system not necessarily in equilibrium and where kinetics plays an important role.Commercial vermiculites heated abruptly at 1000 °C during 1 min transform to mica-like or mica-like coexisting with enstatite, in contrast to the purest Sta. Olalla vermiculite, with only magnesium interlayer cations, which changes to enstatite.