NMR research on deterioration characteristics of microscopic structure of sandstones in freeze-thaw cycles

In order to study the deterioration characteristics of the microscopic structure of sandstones in freeze-thaw cycles, tests of180 freeze-thaw cycles were performed on sandstone specimens. The nuclear magnetic resonance （NMR） technique was applied tothe measurement of sandstone specimens and analysis of the magnetic resonance imaging. Then, the fractal theory was employed tocompute the fractal dimension values of pore development of rocks after different freeze-thaw cycles. The results show that the massand porosity of rocks grow with the increase of freeze-thaw cycles. According to the NMR T2 distribution of sandstones, the poresizes of rock specimens increase after 180 freeze-thaw cycles, especially that of the medium-sized and small-sized pores. The spatialdistribution of sandstone pores after freeze-thaw cycles has fractal features within certain range, and the fractal dimension ofsandstones tends to increase gradually.

Microscopic Structure of Rabbit Hair

[Objective] The paper was to explore the microscopic structure of rabbit hair. [Method] Single rabbit hair with typical features was selected to observe its mi- croscopic structure from tip to root, and its fiber diameter was also measured. [Result] The rabbit hair tip was constituted by scale layer and cortical layer, without medullary layer; the middle part was generally constituted by scale layer, cortical layer and medullary layer; the root had no medullary layer, and the scale layer was wheatear-shaped. This was the property of rabbit hair, which could be used for comparative studies with other animal fiber and species identification. Rabbit hair had developed medullary layer, and fiber diameter was positively related to column number of medullary cavity. The hair generally was single column, and coarse hair was multi-column. Single rabbit hair was the finest in the tip, coarse in the middle and tapering in the root. The diameter difference of various parts was large, and the ex- ternal growth characteristics was spindle-shaped. [Conclusion] Using biological micro- scope method to identify different animal fur and product species is more objective and simple.

Microscopic Structures of Endosperms Before and After Gelatinization in Rice Varieties with Varied Grain Quality

The microscopic structures of the endosperm of indica rice varieties with different quality before and after gelatinization were observed using scanning electron microscope. The results showed that the degree of gelatinization varied in different parts of the grain and in different varieties under the same experimental conditions. The gelatinization of dorsal side was the most complete. Its cells were decomposed totally into puff-like or flocculent materials. The ventral side gelatinized less thoroughly, appearing agglomerate and some cell frames were still visible. The middle part gelatinized most incompletely and the cells were still integrated. Evident differences in gelatinization were observed among different varieties, the dorsal, ventral and middle parts of high quality varieties gelatinized more thoroughly than those of the corresponding parts of low quality varieties respectively. An obvious concavity often appeared in the middle of the cross-section of the low quality grains while the cross-section of high quality grains was normally flat. The same phenomenon was noted when comparing the early maturing indica rice and the late maturing indica rice. Varietal difference of gelatinization in dorsal sides was not as distinct as in middle parts and ventral sides. The difference among dorsal side, middle part and ventral side in gelatinization was greater in low quality grains than that of high quality grains. In addition, a lot of ruptured cells were observed in the cross-section of high quality rice, while few of them could be found in the low quality rice. Apparently, the number of ruptured cells is positively correlated with rice quality. Quality of rice grain also has positive correlation with the rate of water absorption and extension. High rates of water absorption and extension lead to better gelatinization of rice grain, and hence indicate good quality.

Effects of Different Flue-curing Technologies on Microscopic Structure of Flue-cured Tobacco Leaves

[Objective] This study aimed to compare the effects of Chinese quality-improving fragrunce-increasing tobacco flue-curing technology, Chinese three- stage tobaeeo flue-curing technology and Zimbabwean tobaceo flue-euring technology on microscopie structure of flue-cured tobacco leaves to provide theoretical basis for tobacco flue-curing. [ Method ] Middle leaves of tobacco cultivar K326 were collected in Pengshui County of Chongqing City for flue-curing experiment using three flue-curing technologies. Leaf samples were collected regularly in the flue-curing process, to investigate the microscopic structure of flue-cured tobaceo leaves. [ Result] During three flue-curing processes, leaves, palisade tissues and sponge tissues shrank gradually. Three flue-euring processes exhibited significant differ- ences in the peak of tissue shrinkage ： microscopic structure of flue-cured tobacco leaves in Chinese three-stage tobacco flue-curing process shrank earliest, follower by Chinese quality-improving fragrance-increasing tobacco flue-curing process; flue-eured tobacco leaves in Zimbabwean tobacco flue-curing process presented the latest shrinkage. At 84 h post-curing, leaf thickness in three flue-curing processes showed a descend order of Chinese three-stage tobacco flue-curing process 〉 Chinese quality-improving fragrance-increasing tobacco flue-curing process 〉 Zimbabwean tobacco flue-curing process. Upper and lower epidermal cells in Zimb- abwean tobacco flue-curing process ruptured earlier than other two flue-curing processes; eventually, the majority of cells ruptured and mixed with palisade tissues and sponge tissues. In Chinese quality-improving fragranee-increasing tobacco flue-curing process, only a small number of epidermal cells in dried leaves ruptured. Among three flue-curing technologies, Zimbabwean tobacco flue-curing technology exhibited the greatest damage to epidermal cells, followed by Chinese three-stage tobaceo flue-curing technology; Chinese quality-improving fragrance-increasing tobacco flue-curing technology had the minimum damage to epidermal cells. Mese- phyll cross-section exhibited significant morphological changes in stomata. To be specific, at 0 - 12 h post-curing, stomata of tobacco leaves closed with slightly prominent stamatal apparatuses on upper and lower epidermis; at 24 -72 h post-curing, stomata of tobaceo leaves changed gradually from opening to closure with significantly prominent stomatal apparatuses on upper and lower epidermis; at 84 h post-curing, stomata of tobacco leaves closed, and the majority of stomatal appa- ratuses were significantly prominent. In Chinese quality-improving fragrance-increasing tobacco flue-curing process, only a small number of epidermal ceils ruptured at 84 h pest-flue-curing; palisade tissues and sponge tissues shrank almost simultaneously. Significant gaps were observed between palisade tissues and between pal- isade tissues and sponge tissues. Chinese quality-improving fragrance-increasing tobacco flue-curing technology exhibited lower disorder level compared with other two flue-curing technologies. [ Conclusion] Chinese quality-improving fragrance-increasing tobacco flue-curlng technology was conducive to maintaining the micro- scopic structure integrity of flue-cured tobacco leaves and obtaining high-quality flue-cured tobacco leaves.

Connecting microscopic structure and macroscopic mechanical properties of structural materials from first-principles

Computer simulation plays a critical role in connecting microscopic structure and macroscopic mechanical properties of structural material,which is a key factor that needs to be considered in design of such kind of material.Via the quantum mechanics first-principles calculations,one can gain structure,elastic constant,energetics,and stress of selected material system,based on which one is able to predict the mechanical properties or provide useful insights for the mechanical properties of the materials.This can be done either directly or in combination with the empirical criterions.This paper reviews the recent research advances on the attempts to predict the mechanical properties of structural materials from first principles.

Pore-pressure and stress-coupled creep behavior in deep coal:Insights from real-time NMR analysis

Understanding the variations in microscopic pore-fracture structures(MPFS) during coal creep under pore pressure and stress coupling is crucial for coal mining and effective gas treatment. In this manuscript, a triaxial creep test on deep coal at various pore pressures using a test system that combines in-situ mechanical loading with real-time nuclear magnetic resonance(NMR) detection was conducted.Full-scale quantitative characterization, online real-time detection, and visualization of MPFS during coal creep influenced by pore pressure and stress coupling were performed using NMR and NMR imaging(NMRI) techniques. The results revealed that seepage pores and microfractures(SPM) undergo the most significant changes during coal creep, with creep failure gradually expanding from dense primary pore fractures. Pore pressure presence promotes MPFS development primarily by inhibiting SPM compression and encouraging adsorption pores(AP) to evolve into SPM. Coal enters the accelerated creep stage earlier at lower stress levels, resulting in more pronounced creep deformation. The connection between the micro and macro values was established, demonstrating that increased porosity at different pore pressures leads to a negative exponential decay of the viscosity coefficient. The Newton dashpot in the ideal viscoplastic body and the Burgers model was improved using NMR experimental results, and a creep model that considers pore pressure and stress coupling using variable-order fractional operators was developed. The model’s reasonableness was confirmed using creep experimental data. The damagestate adjustment factors ω and β were identified through a parameter sensitivity analysis to characterize the effect of pore pressure and stress coupling on the creep damage characteristics(size and degree of difficulty) of coal.

EFFECTS OF La ON STRUCTURE AND PROPERTIES OF HEAVY RAIL STEEL

The mechanisms of La in heavy rail steel were studied by means of experimental measurements, microstructure observation and theoretical analysis in the present work. For heavy rail steel, the state and the content of La were measured, and the mechanisms and the effects of La on sulfide inclusions, microstracture and properties of steel were determined. Strip-like sulfides disappear in heavy rail steel with La/（O＋S）〉3.50, which is shown that the metallurgical function of modifying sulfide inclusions has been achieved by La. La can fine the grain size of the austenite in heavy rail steel. Under the experimental condition, the plasticity and the impacting toughness of heavy rail steel with 0.005wt% La can evidently be improved.

The Microstructure and Chemical Bonds of β-C_2S Under the High Energy Ball Grinding Function

Using the laser granularity survey technology , logy, X-ray powder diffraction, scanning electron microscopy （SEM） and infrared spectrum anal）sis methods, we studied the microscopic structure and chemical bonds changes of β-C2 S monomineral under the high energy ball grinding function. The result indicates that, continuously under the mechanical power, β-C2 S crystal size would decrease, the micro strain and the effective Beff parameter would increase, and the amorphous phases would be presented. Furthermore, the mechanical power would cause Si-O bond broken and reorganized, the specific surface area would increase, the energy of micro-powder agglomeration vibration would be enhanced and the crystal would be disordered. Finally, β- C2 S was caused to have the mechanochemical change and the activity enhancement.

Quantitative determination of anti-structured defects applied to alloys of a wide chemical range

Anti-structured defects bridge atom migration among heterogeneous sublattices facilitating diffusion but could also result in the collapse of ordered structure.Component distribution Ni（75）AlxV（25-x） alloys are investigated using a microscopic phase field model to illuminate relations between anti-structured defects and composition,precipitate order,precipitate type,and phase stability.The Ni（75）AlxV（25-x） alloys undergo single Ni3V（stage Ⅰ）,dual Ni3Al and Ni3V（stage Ⅱ with Ni3V prior;and stage Ⅲ with Ni3Al prior）,and single Ni3Al（stage Ⅳ） with enhanced aluminum level.For Ni3V phase,anti-structured defects（V（Ni1）,Niy,except V（Ni2）） and substitution defects（Al（Ni1）,Al（Ni2）,Alv） exhibit a positive correlation to aluminum in stage I,the positive trend becomes to negative correlation or smooth during stage Ⅱ.For Ni3 Al phase,anti-structured defects（Al（Ni）,Ni（Al）） and substitution defects（V（Ni）,V（Al）） have a positive correlation to aluminum in stage Ⅱ,but Ni（Al） goes down since stage Ⅲ and lasts to stage Ⅳ.V（Ni） and V（Al） fluctuate when Ni3Al precipitates prior,but go down drastically in stageⅣ.Precipitate type conversion of single Ni3V/dual（Ni3V＋Ni3Al） affects Ni3V defects,while dual（Ni3V＋Ni3Al）/single Ni3 Al has little effect on Ni3Al defects.Precipitate order swap occurred in the dual phase region affects on Ni3Al defects but not on Ni3V.

THE STUDY ON BEHAVIOR OF Al_2O_3-C BRICK FOR BLAST FURNACE AT HIGH TEMPERATURE

In experimental conditions simulating reducing atmosphere in Blast Furnace, the samples of Al 2O 3 C brick were heated at high temperature. Their microscopic structures were observed by Scanning Electric Telescope and rupture and compressive strength measured before and after heating observed the changes. According to these measurements, the reasons causing the changes were analyzed.

Relationship of glass forming ability and local structural properties of liquid Cu-Zr alloys

Molecular dynamics(MD) simulations were performed to investigate the glass forming ability(GFA) and microscopic structural properties of liquid Cu-Zr alloys.Based on the analysis of composition dependences of the reduced glass transition temperatures and the excess volume,we found that the Cu-Zr glasses have the largest GFA at Cu65Zr35 composition.To get more detailed information of local structure,we calculated the pair correlation functions,partial pair correlation functions,the excess entropy,chemical order parameter,coordination number,and Voronoi index of Cu-Zr liquids.We found that there exists an obvious and close relationship among the GFA,the excess entropy calculated using the total pair correlation functions,chemical order parameters,and some Cu centered cluster with Voronoi index <0,2,8,1> and Zr centered cluster with Voronoi index <0,3,6,4>,which all have nonlinear dependences on Cu/Zr concentration and have extreme values at liquid Cu65Zr35 composition.

Underground water biological field＇s variation and geoenvironmental safety in city

In the process of city construction, as a comprised factor of city geological environment, underground water takes the most active part, and its dynamic change is fiercest. The city construction unceasingly disturbs underground water chemical, dynamical, physical and biological field. In return, the four fields＇ changes also can affect the geological environment that city lived by, in other words they affect safety and stability of geological environment. Interaction of underground water and the geoenvironment directly displays in the following two ways： The first is that the underground water and the geological body transfer the energy each other; the second is that the strength balance of geological body is broken. Underground water variation brought about by city construction is the factor which cannot be neglected. Underground water variation on the one hand changes soils or rocks＇ physical, biological, chemical and mechanical properties, then influences the deformation and strength of geological body. On the other hand it changes its own physical, chemical properties and biochemical component. At present, from mechanics aspect, interaction between chemical field and biological field variation of the underground water and the geological body lacks research. Although interaction between them is long-term, slow, but when it compared with water-soil or water-rock interaction in the entire process of formation of rocks or soils or geologic evolution history, the qualitative change of the biological and chemical action of rocks or soils brought about by city construction is remarkable, in this paper, aiming at underground water biological field factor which is easily neglected by people, it analyzes that underground water biological field affects possible mechanism and approach of properties variation of rocks or soils in city construction, brings forward further research method and development direction have been also proposed.

Mechanism investigation on coal and gas outburst: An overview

Coal and gas outburst is a frequent dynamic disaster during underground coal mining activities.After about 150 years of exploration,the mechanisms of outbursts remain unclear to date.Studies on outburst mechanisms worldwide focused on the physicochemical and mechanical properties of outburst-prone coal,laboratory-scale outburst experiments and numerical modeling,mine-site investigations,and doctrines of outburst mechanisms.Outburst mechanisms are divided into two categories:single-factor and multi-factor mechanisms.The multi-factor mechanism is widely accepted,but all statistical phenomena during a single outburst cannot be explained using present knowledge.Additional topics about outburst mechanisms are proposed by summarizing the phenomena that need precise explanation.The most appealing research is the microscopic process of the interaction between coal and gas.Modern physical-chemical methods can help characterize the natural properties of outburst-prone coal.Outburst experiments can compensate for the deficiency of first-hand observation at the scene.Restoring the original outburst scene by constructing a geomechanical model or numerical model and reproducing the entire outburst process based on mining environment conditions,including stratigraphic distribution,gas occurrence,and geological structure,are important.Future studies can explore outburst mechanisms at the microscale.

Mechanisms of shale hydration and water block removal

Shale samples of Silurian Longmaxi Formation in the Changning area of the Sichuan Basin, SW China, were selected to carry out scanning electron microscopy, CT imaging, high-pressure mercury injection, low-temperature nitrogen adsorption and imbibition experiments to compare the hydration characteristics of montmorillonite and illite, analyze the main factors affecting the water block removal of shale, and reveal the mechanisms of pore structure evolution during shale hydration. The hydration characteristics of shale are closely related to the composition of clay minerals, the shale with high illite content is not susceptible to hydration and thus has limited room for pore structure improvement;the shale with high montmorillonite is susceptible to hydration expansion and thus has higher potential of pore structure improvement by stimulation;the shale with high illite content has stronger imbibition in the initial stage, but insufficient diffusion ability, and thus is likely to have water block;the shale with high montmorillonite content has weaker imbibition in the initial stage but better water diffusion, so water blocking in this kind of shale can be removed to some degree;the shale reservoir has an optimal hydration time, when it is best in physical properties, but hydration time too long would cause damage to the reservoir, and the shale with high illite content has a shorter optimal hydration time;inorganic cations can inhibit the hydration of clay minerals and have stronger inhibition to illite expansion, especially K^(+);for the reservoir with high content of montmorillonite, the cation content of fracturing fluid can be lowered to promote the shale hydration;fracturing fluid with high K^(+) content can be injected into reservoirs with high illite content to suppress hydration.

Fractal characteristic of microscopic pore structure of tight sandstone reservoirs in Kalpintag Formation in Shuntuoguole area,Tarim Basin

Using the fractal geometry method,the microscopic pore structures of tight sandstone reservoirs in Kalpintag Formation of Shuntuoguole area in Tarim Basin were conducted fractal characterization on the base of test analysis data such as physical property,cast thin section,scanning electron microscope and mercury injection,and the genetic mechanism of pore structure heterogeneity was investigated.The storage spaces are dominated by intergranular dissolved pore,intragranular dissolved pore and residual intergranular pore,and the throat type consists of the necking throat,lamellar throat,curved lamellar throat and tube-shaped throat.The microscopic structure type includes Type Ⅰ(fractal dimension≤2.350),Type Ⅱ(2.350<fractal dimension<2.580),Type Ⅲ(fractal dimension>2.580)and fracture type.The most favorable reservoirs with Type-Ⅰ microscopic pore structure are mainly distributed in the Upper Member of Kalpintag Formation,while the reservoirs with Type-Ⅱ and Type-Ⅲ microscopic pore structures are mainly in the Lower Member of Kalpintag Formation.The sedimentation controls the heterogeneity of microscopic pore structure,and the differences on composition and particle size of sandstone lead to differentiation of microscopic pore structures.The Lower Member of the Kalpintag Formation experiences stronger compaction and cementation but weaker dissolution than the Upper Member of the Kalpingtag Formation,and thus the microscopic pore structure of Upper Member of the Kalpintag Formation is significantly worse that of the Lower Member o the Kalpingtag Formation.The Upper Member of the Kalpintag Formation with high content of brittle mineral develops microscopic fractures due to tectonic rupture,thus the permeability is improved and the heterogeneity of microscopic pore structures is enhanced;but the Lower Member of Kalpintag Formation is characterized by attrition crushing of particles and strong compaction.

Pore and fracture characteristics of Cretaceous tight reservoir and its control effect on hydrocarbon accumulation in the Liuhe Basin

Tight oil and gas in the Cretaceous has been found in the Liuhe Basin,but the rules of tight reservoir and oil and gas accumulation are not clear.This paper discusses the developmental characteristics and evolution law of pores and fractures in the Cretaceous tight reservoir in the Liuhe Basin,and reveals its controlling effect on tight oil and gas accumulation.The results show that intercrystalline pores,intergranular pores and dissolution pores are scattered and only developed in shallow tight reservoirs,while microfractures are developed in both shallow and deep layers,which are the main type of reservoir space in the study area.The results of mercury intrusion porosimetry and nitrogen gas adsorption show that with the increase of depth,the proportion of macropores(microcracks)increases,while the proportion of micropores decreases.There are two stages of microfractures developed in the study area,corresponding to the initial fault depression stage from late Jurassic to early late Cretaceous and compressional uplift at the end of late Cretaceous.According to the principle of“inversion and back-stripping method”,combined with the data of optical microscopy and inclusions,the time of each key diagenesis and its contribution to porosity are revealed,and the porosity evolution history of reservoirs in different diagenetic stages is quantitatively restored.The porosity reduction rate of compaction can reach more than 80%,which is the main reason for reservoir densification.The relationship between pore evolution history and oil and gas accumulation history reveals that during the oil and gas filling period of the Xiahuapidianzi Formation(90-85 Ma),the reservoir porosity is only 1.15%,but the development of microfractures in the first stage of the reservoir is conducive to oil and gas accumulation.

Morphology of Barium Hydrogen Phosphate Formation Induced by Phosphate-Mineralization Microbe

Phosphate-mineralization microbe was chosen to study the influences of bacterial mixture,filtrate,bacteria solution,bacterial body and bacterial secretion on barium hydrogen phosphate crystal formation.The chemical compositions and structures of samples were characterized with scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,and X-ray diffraction techniques（XRD）,revealing that the crystal morphology of barium hydrogen phosphate was dumbbell-shaped pattern,nanoparticles via aggregate clusters,irregular sphere with different sizes.The results indicated that bacterial body and bacterial secretion could induce the formation of irregular quadrilateral and spheres,respectively.But the effect of bacterial secretion was stronger than that of bacterial body when induced barium hydrogen phosphate crystal in bacteria solution.However,the crystals form could be affected only in bacterial mixture,but filtrate could induce the formation of nanoparticles.As a result,the bacteria and metabolites play an important role in the process of crystal nucleation,growth,and accumulation of barium hydrogen phosphate.

Fine description of unconventional clastic oil reservoirs

The latest researches reveal that studies on unconventional clastic oil reservoirs in China generally lag far behind those in other countries in respect of content and methodology.This study presents the definition and classification of unconventional oil reservoirs and analyzes the problems in the fine description of unconventional oil reservoirs.The key content of the fine description of unconventional oil reservoirs is summarized from four aspects:fine fracture characterization based on fine structure interpretation,reservoir architecture characterization based on sedimentary facies,characteristics of nanoscale microscopic pore structure of reservoir,and evaluation of source rock and“sweet spot zone”.Finally,this study suggests that development of fine description of unconventional clastic oil reservoirs in the future should focus on rock brittleness analysis and fracture modeling,geophysical characterization of unconventional clastic oil reservoirs,fluid description of tight reservoirs,and physical/numerical simulation experiments of unconventional oil reservoirs.

Characterization of cake layer structure on the microfiltration membrane permeability by iron pre-coagulation

A cake layer is formed by coagulation aggregates under certain transmembrane pressure in the coagulation-microfiltration （MF） process. The characteristics of humic acid aggregates coagulated by different iron-based coagulants, such as charge, size, fractal dimension and compressibility, have an effect on the cake layer structure. At the optimum iron dose of 0.6 to 0.8 mmol/L for ferric chloride （FC） and polymer ferric sulfate （PFS） pre-coagulation, at the point of charge neutralization for near zero zeta potential, the aggregate particles produced possess the greatest size and highest fractal dimension, which contributes to the cake layer being most loose with high porosity and low compressibility. Thus the membrane filterability is better. At a low or high iron dose of FC and PFS, a high negative or positive zeta potential with high charge repulsion results in so many small aggregate particles and low fractal dimension that the cake layer is compact with low porosity and high compressibility. Therefore the membrane fouling is accelerated and MF permeability becomes worse. The variation of cake layer structure as measured by scanning electric microscopy corresponds with the fact that the smaller the coagulation flocs size and fractal dimension are, the lower the porosity and the tighter the cake layer conformation. This also explains the MF membrane flux variation visually and accurately.

Accurate design and synthesis of nonlinear optical crystals employing KBe_(2)BO_(3)F_(2) as structural template

In spite of decades of great efforts,it is still very challenging to realize accurate design and synthesis of second-order nonlinear optical(NLO)crystals.KBe_(2)BO_(3)F_(2)(KBBF)is the sole NLO material that can output deep-ultraviolet light by direct second-harmonic generation process,so it is an ideal choice to use KBBF as the structural template to design environment-friendly candidates with better growth habit based on the reported compounds.In this review,we will elaborate the accurate design and synthesis of high-performance NLO ma-terials from the perspective of microscopic crystal structure based on KBBF,hoping to provide deep understanding on how to rationally design and synthesize targeted compounds efficiently and quickly.In addition,according to multiple requirements on ultraviolet NLO crystals,including second-harmonic generation,cut-off edge,and birefringence,we propose a new concept so-called quality factor to comprehensively evaluate the overall per-formance of new ultraviolet NLO materials.This concept would help to directly and readily evaluate the ability of an ultraviolet NLO material to achieve practical NLO output.