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The greatest difficulty of grouting fractures under flowing condition was that the slurry was easily washed out by the flowing. To raise the sealing efficiency (SE) and dynamic flowing resistance of slurry, carbon fiber was added into the grout and a new grout for flowing water environmental was provided. Contrast tests and SEM tests were conducted to investigate the effect of carbon fiber. The result showed that the solidification velocity and dynamic flowing resistance increased with an increase of carbon fiber content due to the stochastic distribution and great surface friction of carbon fiber. In addition, a series of orthogonal tests were conducted to investigate the effect of some factors on the SE. The result showed that the SE decreased with the increase of initial flow speed and aperture width, and it increased with the increase of cement water ratio and additive content. Finally a fitting equation was acquired to provide reference to the practical engineering.

采用改性共沉淀法合成了La 9.33 Si 6 O 26 -10wt% Zr 0.86 Y 0.14 O 1.92 两相共存的氧离子导电复合材料, 利用X射线衍射、扫描电子显微镜、交流阻抗技术分别表征了材料的相组成、微观组织和离子导电性. 结果表明, 复合材料粉体平均晶粒尺寸为35 nm, 烧结块体的平均颗粒尺寸为500 nm; 在300~700℃温度范围内, 复合材料的导电率均高于La 9.33 Si 6 O 26 或Zr 0.86 Y 0.14 O 1.92 单相材料, 且700℃时比La 9.33 Si 6 O 26 高出1个数量级. 结合交流阻抗谱及电模量谱对复合材料的导电机理进行了分析讨论.

Novel intelligent hydrogels containing β-cyclodextrins were prepared by tandem physical and chemical crosslinking method based on Diels–Alder reaction. First, dienophile-functionalized cyclodextrins (HCD–AMI) were synthesized by the coupling reaction of hydroxyethyl-β-cyclodextrins and N-maleoyl alanine (AMI); diene-functionalized polymers (PFMIPA) were synthesized by free radical copolymerization of N-isopropylacrylamide and furfuryl amine maleic acid monoamide, a novel monomer synthesized in our lab. Then, the LCSTs of the PFMIPA were estimated by transmittance measurements of copolymer solutions. After the as-synthesized PFMIPA and HCD–AMI were dissolved separately in water and mixed, the hydrogels with physical crosslinks formed quickly within 10 s at 37 °C. Subsequently, chemical crosslinks came into being gradually due to Diels–Alder reaction. Therefore, there are both physical crosslinks and chemical crosslinks in as-prepared hydrogels, resulting in the improvement of the mechanical strength of the hydrogels. And the in vitro degradation behaviors of the resultant hydrogels were given a pilot study. A general gravimetric method was used to study the swelling behavior of the hydrogels. It was found that the hydrogels showed good pH/temperature-sensitivity. The strategy described here has several advantages for preparing intelligent hydrogels including tunable gelation rate, mild reaction conditions, no initiator or catalyzer, and no organic solvent. We believe that this novel, potentially biocompatible hydrogels could have biomedical applications, especially in the area of tissue engineering and drug-controlled release carriers.

N -vinyl-2-pyrrolidone-based hydrogels were prepared by the Diels–Alder reaction in water for the first time. Copolymers of N -vinyl-2-pyrrolidone(VP) and furfuryl methacrylate(FM) were synthesised by free radical polymerisation in toluene at 70 °C by using 2,2′-azobisisobutyronltrile as an initiator. Polymeric dienophile (PEG–AMI) was prepared from N -alaninyl maleimide (AMI) and poly(ethylene glycol) (PEG) by using N , N ′-dicyclohexylcarbodiimide (DCC) as a dehydrating agent. The prepared dienes and dienophile were then dissolved in water and mixed, leading to gelation via Diels–Alder reaction after some time. The gelation times of different copolymers and PEG–AMI in different solvents and at different temperatures were measured by the vial inversion method, and the swelling behaviour of dried hydrogels was studied using a general gravimetric method. The gelation time was shorter in water than in organic solvents, and the gelation time decreased with the increase of temperature and FM content in copolymers. Conversely, the swelling ratios increased with the decrease of temperature and FM content in the copolymers. Disassembly experiments suggested that N , N -dimethylformamide (DMF) could accelerate the retro-DA reaction.

The study reports a facile method of preparing poly(N-isopropylacrylamide)- based hydrogels by means of the Diels–Alder reaction. First, polymeric dienes were synthesized by free radical copolymerization between N-isopropylacrylamide (NIPA) and furfuryl methacrylate (FM), with 2, 2′-azobisisobutyronitrile (AIBN) as an initiator, and polymeric dienophile was obtained by a coupling reaction of poly(ethylene glycol) (PEG) and N-maleoyl- l -leucine (LMI) under N, N′-dicyclohexylcarbodiimide (DCC). Afterwards, the resultant dienes and dienophiles were dissolved in water and put in a refrigerator remaining a temperature of 9 °C, gelation via Diels–Alder reaction was observed after some time. The samples obtained at different steps were characterized by FTIR, NMR, GPC, SEM, CD, etc. It was found that LCST of copolymers decreases with the increase of FM content in copolymers. And the disassembly time of the hydrogels is closely related to the temperature and the solvents used. The swelling behavior study by gravimetric measurement indicates the hydrogels possess thermosensitivity and exhibit considerable swelling in water. Due to the simplicity of synthesis and no need for initiator or catalyzer and organic solvent, the strategy described here could find a promising application in the preparation of hydrogels.

用化学共沉淀法制备了Ce0.8Sm0.2O1.9-La9.33Si6O26纳米复合氧离子导电材料,通过X射线衍射和透射电子显微镜对合成材料的相结构进行了分析,利用交流阻抗分析测试研究了材料的离子导电性.结果表明,纳米复合材料的煅烧粉末的平均晶粒尺寸为20nm、烧结陶瓷体的平均晶粒尺寸为44nm;700℃时,纳米复合导电体的离子导电率为0.25Ω/cm;在整个测试温度范围内,纳米复合导电体比纯La9.33Si6O26提高了3个以上数量级,并高于纯相Ce0.8Sm0.2O1.9的导电性.

A method of approximating the pile-up contact perimeter as a semi-ellipse originally developed for soda-lime glass, has been investigated for its applicability to other materials including work-hardened copper, Zr-based bulk metallic glass, strontium fluoroapatite, tungsten carbide, silicon nitride and aluminium oxide. The study revealed that all the materials formed pile-ups during nanoindentation. The elastic modulus and hardness values obtained after correcting for the pile-up contact area using the semiellipse approximation were,consistent with those found in the literature.

The contact residual stress field created by a Vickers indentation is a micro-size region of high and varying stresses. Stress relaxation studies in such a micro-region may not be accessible to the conventional methods of investigation. In this paper the elastic response during nanoindentation has been used to study the isothermal stress relaxation of a Vickers residual stress field in soda-lime glass at 540 and 630 °C. At each temperature, the stress relaxation profile varied from one location of the stress field to the other suggesting non-linear response to stress. Also, the relaxation profiles at identical positions were different for the two temperatures suggesting that the Vickers residual stress field is not a thermorheologically simple region of material.

Strontium and magnesium doped lanthanum gallate La0.85Sr0.15Ga0.85Mg0.15O3-delta (LSGM) oxygen ionic conducting ceramics were prepared by a steric entrapment synthesis (SES) method, which is a poly ...

An empirical relationship for estimating the pile-up contact area from the contact stiffness, S and the contact depth, hc, has been developed. This was achieved first by using the atomic force microscope to image nanoindents made with the Berkovich indenter in soda-lime glass and approximating the pile-up contact perimeter as a semi-ellipse. Then, by determining the pile-up contact area for several peak indentation loads, a correlation was found between the pile-up contact area and the load used to generate it. The importance of this new method of determining the pile-up contact area is that the need for indent imaging is made completely redundant, since the contact stiffness is a quantity that is routinely obtained during nanoindentation data analysis. Elastic modulus of soda-lime glass of 70 ± 1.5 GPa is measured with loads ranging from 20 to 500 mN. The hardness measured also falls within the range of values, 5.2–5.9 GPa, normally quoted in the literature for the glass.

BaTiO3 ceramics doped by single dopants of Sm2O3, Ho2O3, Bi2O3, La2O3, CeO2 and Ta2O5, respectively, were prepared and aged in air. The room-temperature resistivity was measured and the relationship between resistivity change versus ageing time was determined. The electrical resistivity of Bi- and Ta-doped samples decreases at the early ageing stage, and then increases with the ageing time; the other doped ceramics display a monotonous increase of the resistivity with ageing time. The electrical properties and ageing characteristics are analyzed by considering interior oxidation and reduction reactions and the electronegativity of the doping elements.

The electrical resistivity of (Ba 0.69 Pb 0.31 )TiO 3 PTCR ceramic thermistors aged at temperatures of 175, 200, 250 and 300 °C, respectively, were measured. When the samples were aged at temperatures of 175 and 200 °C, room-temperature resistivity decreased at the initial ageing stage, and then increased with the ageing time. The samples displayed a monotonous rise of the room-temperature resistivity when the ageing treatments were performed at 250 and 300 °C. PTCR effects showed different characteristics after different ageing treatments. These ageing characteristics were analyzed by considering interior oxidation and reduction reactions.

Sm2O3-doped barium titanate ceramics with a positive temperature coefficient of resistivity (PTCR) were synthesized by solid-state reaction sintering. The electrical properties are related to the d ...

The influence of stress on the elastic modulus E and hardness H in soda-lime glass was studied in the Vickers residual stress field by nanoindentation. The Oliver–Pharr method of analysis first gave higher values of E and H, but after correcting for the pileup contact areas around the nanoindents, results consistent with literature values were obtained at regions in the stress field where the stresses were either low or close to zero. Determination of the pileup contact areas was made possible by the use of the atomic force microscope, which has facility for generating cross-section images of the indents. The elastic modulus was found to decrease with stress, which is explained with reference to the influence of applied stresses on the Si–O–Si bond angle. The hardness on the other hand did not depend on the stresses except in the region very close to the edge of the Vickers indent where the stresses are high.

The phase precipitated in an Mg-Y-Nd alloy during ageing was studied using electron microscopy. Observations were performed along the orientations paralleling to [0001] and [11 (2) over bar0] zone axes of the matrix. The results showed that the platelike p phase has three variants growing along three directions of the matrix, the beta phase grew faster along (alpha) and (alpha) directions than along the third direction ( ). The morphology of the beta phases was illustrated according to the analysis of the directional misfit between the beta phase and the matrix. (C) 2004 Elsevier B.V. All rights reserved.

(Ba0.69Pb0.31)TiO3 ceramics were prepared using Al2O3, SiO2, additives and excess of TiO2 (AST). The characteristics of positive temperature coefficient of resistivity (PTCR) was studied and the corresponding microstructures were investigated using atomic force microscopy and scanning electron microscopy. The results showed that the PTCR effect was related to the AST additives. The maximum value of resistivity in the ceramics with lower content of or without Al2O3 and SiO2 additives was much lower than in those with AST additives. Ceramics with low AST content, which were heated by electric field to a temperature much higher than their Curie temperature, lost the PTCR effect after the electric field stimulation. The microstructure observations revealed that re-crystallization took place in the ceramics with lower content of or without AST additives resulting in the loss of the PTCR effect.

High frequency dielectric measurements (300 kHz–3 GHz) have been used to assess the water uptake by bonded composite resin joint structures. Comparison of exposed and dry joints demonstrated that a correlation exists between changes with time in the dielectric properties of the joints and the extent of water uptake in the matrix as determined gravimetrically. Diffusion of water into the joints is discussed in terms of various models. The changes in mechanical properties as a function of water uptake are reported over an extended period of time. The use of dielectric measurements as a non-destructive examination method for the assessment of water ingress into joint structures is demonstrated.

Analysis using a network analyser of the electrical response between 300 kHz and 200 MHz for a range of model waveguide structures is discussed. The structures chosen illustrate the variations to be expected in real adhesive bonds and include changes in bond line thickness, width and electrical conductivity of the substrate. A simple theoretical model was used to simulate the time domain data and very good agreement between experiment and theory was observed. Deficiencies in the model appeared when it was used to simulate frequency domain data, and the limitations of these calculations are critically discussed. The accuracy to which this method can be used to calculate the dielectric permittivity was assessed from a study of a number of polymers with well-defined dielectric characteristics. Parallel plate structures were fabricated using low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), polycarbonate (PC) and polymethyl methacrylate (PMMA). Good agreement between literature and experiment was observed in all cases, validating the dielectric permittivity values obtained using this approach. This paper illustrates the potential of nondestructive electrical measurements to provide structural and quantitative permittivity information on adhesive joint structures.

The effects on the dielectric characteristics of aluminium-adhesive bonded joint structures with different surface treatments on exposure to moisture at elevated temperatures are reported. Analysis of the frequency domain data as a function of the exposure time allows three major ageing processes to be identified; plasticization of the adhesive, changes in the state of interfacial oxide and generation of disbonded areas. Time domain data allows identification of regions where changes in the characteristics of the bond have occurred and complements the data obtained from frequency domain data. Mechanical tests on joints aged for 733 days indicate a large decrease in the shear strength has occurred consistent with the detection of marked changes in the dielectric traces. Anodization of the substrate increases the durability of joints in comparison with etched samples. This study illustrates the potential of this method for in-situ characterization of changes occurring both within the adhesive and the adhesive substrate interface.

Applications of high-frequency dielectric measurements (300 kHz to 3 GHz) to the non-destructive examination (NDE) of composite structures are discussed. Preliminary data indicate that the method, previously used for aluminium bonded structures, can be applied to bonded carbon fibre composite structures. Water ingress into the bond structure was observed to influence both the time- and the frequency-domain data. Comparison of exposed and dry joints demonstrated that a good correlation exists between changes with time in the dielectric properties of the composites and the extend of water uptake in the matrix. Parallel gravimetric measurements were also performed. Diffusion of water into the composite structures is discussed in terms of various models. This paper demonstrates that this NDE method may be used for assessment of the water content in the matrix and has general applicability to the study of carbon-reinforced matrix materials.

Dielectric techniques have the potential of allowing observation of changes in the dipole mobility within an adhesive joint structure as a result of its exposure to a warm humid environment. Water molecules absorbed by an adhesive resin will exhibit a series of distinct relaxation features, which are characteristic of the environment in which the molecules are located. Hydration of the surface oxide of an aluminium-epoxy joint will produce a distinctive dielectric relaxation at approximately 1 MHz which is quantitatively related to the amount of hydroxide formed. Data on aged adhesive joints indicates that the dielectric technique has potential for the study of the changes occurring within the joints and the technique may be also used for studies of carbon fibre - epoxy - carbon fibre structures.

A Ti-50.4 at.%Ni alloy ingot was prepared and rolled into plate of 1-mm thickness at 1025 K. The hot-rolled plate was cold rolled at room temperature to the extent of 50% reduction in thickness and annealed at 573, 693 and 753 K, respectively. The investigated results revealed that 693 K annealed specimen had a homogeneous nanocrystalline structure with the grain size about 30 nm and showed the best superelasticity. The relation between the microstructure and the superelasticity has been discussed in the present report. (C) 2002 Elsevier Science B.V All rights reserved.