Search

This investigation focuses on the change of C-S-H gels in Portland cement (PC) paste and PC/ground granulated blast-furnace slag (GGBFS) blended paste at elevated temperature up to 800 °C. Spark-like phase, which might be spurrite, can be found in the inner product of C3S in PC paste when the temperature is higher than 600 °C. The gels in PC paste show an obvious change in composition in comparison with the gels in GGBFS blended paste at elevated temperature. After 600 °C, the continuous decomposition and shrinkage of C-S-H gels results in the increase of small pores (10–40 nm) in both pastes. The nitrogen adsorption results show that some gels, which should be C-A-S-H in GGBFS blended paste, are quite stable at high temperature. The results of this study provide a comprehensive understanding of the different behavior between gels in PC paste and GGBFS blended paste at high temperature.

The presence of equilibrium intergranular films (IGFs) in metallic systems has long been postulated; compelling evidence for this idea, however, is still lacking. Herein differential scanning calorimetry, in the−60°C to 70°C temperature range, on bulk and Cr2GaC powders was carried out. A sharp endothermic trough, roughly 50°C below the melting point of bulk pure Ga, in the powdered samples was taken to be strong evidence for the presence of IGFs in the latter. The troughs for the sintered body were much more diffuse suggesting that in this case, a distribution of grain boundary thicknesses exists. A temperature dependent adsorption energy is postulated to explain the reversible extrusion and resorption of 100 μm thick Ga micro-pillars.

Multiple target magnetron sputtering technique was employed for the deposition of (Cr,V)2AlC thin films, on the substrate of Si wafer at temperatures ranging from ambient to 840 K. The chemical composition and crystal structure of the deposited thin films were analyzed, surfaces as well the cross sections observed. The experimental results demonstrated that the temperature of the substrate does not affect the chemical composition of the deposited thin films. Deposition at room temperature or moderate elevated temperatures was found to result in amorphous films, whereas crystalline MAX phase thin films were obtained at high temperature. The transition of the substrate temperature was found to be around 743 K. The thin films deposited at temperatures below the transition showed the featureless flat surfaces. At high substrate temperatures, crystalline MAX thin films were formed. When deposited at temperatures near the transition, amorphous/nanocrystalline double layer thin films were deposited.

KBD is an endemic disease affecting the epiphyseal growth plate and articular cartilage of multiple joints, resulting in extremities’ deformation and skeletal dysplasia. More attention has been paid to the visible deformed extremities instead of inconspicuous spinal condition. There is a lack of reports concerning the spinal radiological features, especially for the atlantoaxial joint. The aim of this paper is to report a case of a Kashin–Beck disease (KBD) patient diagnosed with atlantoaxial subluxation, concomitant with separated odontoid process fused to the enlarged anterior arch of the atlas. We report the case of a 60-year-old woman with 54 years’ history of KBD complaining of occipitocervical pain, decreasing motor strength and sensory function of both upper and lower extremities. Subsequent radiological examinations of lateral plain radiography, computed tomography scans and magnetic resonance imaging were performed to reveal these rare characteristics of atlantoaxial joint in this patient. Then, we review the associated articles to postulate whether this anomaly is accidental or linked in a KBD patient. She had an extremely rare variant with three aspects of characteristics: atlantoaxial subluxation concurrent with severe spinal canal stenosis and spinal cord compression, odontoid process separating from the body of axis, and the enlarged anterior arch of the atlas fusion with odontoid process. Comparing with the congenital anomaly of atlantoaxial joint, we postulated that this aetiology of anomaly might be linked to the acquired form attributed to the histopathology of KBD, rather than an accidental event. The anomaly of atlantoaxial joint might occur in KBD patients. Larger numbers of KBD candidates with earlier symptoms are recommended for radiological examinations of atlantoaxial joint, especially for the adolescents. Spinal surgeons are suggested to involve the research of the spinal anatomy and variation for the prevention and earlier therapy for KBD patients.

Kashin-Beck disease (KBD) is an endemic degenerative osteoarthropathy. The mycotoxin of T-2 toxin is extensively accepted as a major etiological contributor to KBD. However, its function and mechanism in KBD remains unclearly elucidated. Here, T-2 toxin treatment induced chondrocyte injury in a time- and dose-dependent manner by repressing cell viability and promoting cell necrosis and apoptosis. Importantly, T-2 suppressed the transcription of type II collagen and aggrecan, as well as the release of sulphated glycosaminoglycan (sGAG). Furthermore, exposure to T-2 enhanced the transcription of matrix metalloproteinases (MMPs), including MMP-1, -2, -3 and -9. In contrast to control groups, higher expression of insulin-like growth factor binding protein 2 (IGFBP2) was observed in chondrocytes from KBD patients. Interestingly, T-2 toxin caused a dramatical elevation of IGFBP2 expression in chondrocytes. Mechanism analysis corroborated that cessation of IGFBP2 expression alleviated T-2-induced damage to chondrocytes. Simultaneously, transfection with IGFBP2 siRNA also attenuated matrix synthesis and catabolism-related gene expressions of MMPs. Together, this study validated that T-2 toxin exposure might promote the progression of KBD by inducing chondrocyte injury, suppressing matrix synthesis and accelerating cellular catabolism through IGFBP2. Therefore, this research will elucidate a new insight about how T-2 toxin participate in the pathogenesis of KBD.

Bi 2 Se x Te 3− x crystals with various x values were grown by Bridgman method. The electrical conductivity, σ , was found to decrease with increasing Se content. The highest σ of 1.6 × 10 5 S m −1 at room temperature was reached at x = 0.12 with a growth rate of 0.8 mm h −1 . The Seebeck coefficient, S , was less dependent on Se content, all with positive values showing p-type characteristics, and the highest S was measured to be 240 μV K −1 at x = 0.24. The lowest thermal conductivity, κ , was 0.7 W m −1 K −1 at x = 0.36. The electronic part of κ , κ el , showed a decrease with increasing Se content, which implies that the hole concentration as the main carriers was reduced by the addition of Se. The highest dimensionless figure of merit, ZT , at room temperature was 1.2 at x = 0.36, which is attributed to the combination of a rather high electrical conductivity and Seebeck coefficient and low thermal conductivity.

The MAX phases are a group of layered ternary compounds with the general formula Mn+1AXn (M: early transition metal; A: group A element; X: C and/or N; n = 1–3), which combine some properties of metals, such as good electrical and thermal conductivity, machinability, low hardness, thermal shock resistance and damage tolerance, with those of ceramics, such as high elastic moduli, high temperature strength, and oxidation and corrosion resistance. The publication of papers on the MAX phases has shown an almost exponential increase in the past decade. The existence of further MAX phases has been reported or proposed. In addition to surveying this activity, the synthesis of MAX phases in the forms of bulk, films and powders is reviewed, together with their physical, mechanical and corrosion/oxidation properties. Recent research and development has revealed potential for the practical application of the MAX phases (particularly using the pressureless sintering and physical vapour deposition coating rout...

Many studies have demonstrated that apoptosis is involved in the development of disc degeneration. The initiator caspase 9 is activated through the apoptosome-driven intrinsic apoptotic pathway. The present study aimed to assess the potential association between the caspase 9 gene polymorphism and lumbar disc herniation (LDH) susceptibility, as well as severe grades of disc degeneration in the Han population in northern China. Genotyping was performed using the polymerase chain reaction and polymorphism was analyzed by restriction endonuclease cleavage in 387 patients with LDH and 412 control subjects. The allelic frequencies of caspase 9 Ex5+32 A were 0.483 and 0.391 in case patients and control subjects, respectively. Compared to those with the AA genotype, subjects with the GA/GG genotype have a higher risk to develop LDH (odds ratio 1.91; 95% confidence interval 1.29-2.81). Moreover, the GA/GG genotype was found to contribute to the risk of more severe grades of disc degeneration, as observed in magnetic resonance imaging scan. In conclusion, this study suggests that the single nucleotide polymorphism in the caspase 9 Ex5 + 32 G/A may be associated with LDH and disc degeneration in the Han population of northern China.

As an invited paper with the designated title to this focused session, this is to introduce the pulse discharge sintering process applied for the sintering and/or synthesis of a few representative MAX phases, such as Ti 3 SiC 2 , Ti 3 AlC 2 , Ti 2 AlC, Ti 2 AlN, Cr 2 AlC, Cr 2 GaC, Ti 2 GaC, as well as the MAX-based solid solutions and some composites. The effects of processing parameters on the synthesis reactions, densification, microstructure, as well as the properties have been investigated. This paper not only briefly reviews our synthesis work on the MAX phases but also presents new results such as the comparison of PDS with conventional hot pressing, the newly obtained results on the synthesis of Cr 2 GaC, Ti 2 GaC, as well as some solid solutions and composites. With the results presented herein as summarized in tables and figures, none of which were published elsewhere, this article aims at a better understanding of the PDS process in the research and development of the MAX phases and related materials.

Ti 3 SiC 2 –TiC composites were fabricated by pulse discharge sintering technique using three different sets of powder mixtures, i.e. Ti/Si/TiC (TC30), Ti/Si/C/TiC (SI30) and Ti/Si/C (TSC30). Based on X-ray diffraction (XRD) analysis and microstructural observations, starting powder reactants were found to have little effect on phase content but strong influence on the microstructure in terms of phase distribution. The phase distribution mainly relies on the heat released from reaction and the liquid phase content formed during sintering. The mechanical properties of the fabricated dense samples demonstrate that more homogeneous phase distribution, available by choosing the starting reactants of SI30, results in higher flexural strength, whereas the Vickers hardness is almost independent of the microstructure. The enhanced flexural strength in sample SI30 sintered at 1400 °C is mainly attributed to the homogeneous TiC distribution in the microstructure.

In this paper, the effect of high-temperature vacuum annealing on the dynamic phase stability and phase transition of Ti3AlC2 at up to 1550°C was studied using in situ neutron diffraction. The decomposition of Ti3AlC2 into TiCx at an elevated temperature was observed to occur through the continuous sublimation of Al and Ti species in a dynamic environment of high vacuum. The rate of decomposition decreased with increasing temperature, resulting in negative apparent activation energy (i.e., −71.9 kJ/mol). Depth profiling of vacuum-annealed Ti3AlC2 by grazing-synchrotron radiation diffraction has revealed a graded composition of TiCx at the near-surface.

During pulse discharge sintering (PDS) of Ti/SiC/C powder mixture, combustion synthesis reactions occurred at heating rates above 20 °C/min. With an increase in heating rate, combustion synthesis occurred at higher temperatures. The essential of this combustion reaction is the liquid reaction between Ti and formed Ti 5 Si 3 . The exothermic TiC formation during PDS process promotes this liquid reaction. We have found that the combustion reactions alone did not finish the formation reactions for Ti 3 SiC 2 , and further heating following the combustion reactions is necessary for the synthesis process of Ti 3 SiC 2 .

Summary To identify HLA-B*15 subtypes distribution in Han population in Beijing, People’s Republic of China, 826 unrelated healthy individuals were typed using the polymerase chain reaction-sequence-based typing method. Within the 246 HLA-B*15 positive individuals, 29 HLA-B*15 alleles were identified, the most predominant of which is B*1501 (40.07%), followed by B*1502 (12.87%), B*1511 (12.87%), B*1518 (9.19%) and B*1532 (3.31%). The distribution of HLA-B*15 subtype frequencies was compared between the Beijing Han, eight other Chinese ethnic minorities and six Chinese populations covering the mainland of China, Taiwan, Hong Kong and Singapore. A neighbor-joining phylogenetic tree was constructed and revealed that the Beijing Han population clustered into the northern populations group and had a closer relationship with northern Han and Hui than with southern Han or other ethnic minorities. These results thus provide useful information that can be used in anthropology, selection for bone marrow transplantation as well as in disease-association study, such as in carbamazepine (CBZ)-induced Stevens–Johnson syndrome and toxic epidermal necrolysis.

We have performed first-principles study on phase stability and compression behavior of Ti 2 SC and Ti 2 AlC. Ti 2 SC is found to be more stable than Ti 2 AlC due to its deeper pseudogap, lower density of states at the Fermi level and stronger Ti d–S p hybridization. Ti 2 SC shows higher stiffness than Ti 2 AlC when compressed. The calculated bulk modulus is 181 and 162 GPa for Ti 2 SC and Ti 2 AlC, respectively. The bond strength of Ti 2 SC and Ti 2 AlC becomes greater at high pressures. However, no evidence for any change in the nature of the bonding under pressure is observed.

We have performed theoretical studies on the elastic and thermodynamic properties of the solid solution: Ti 2 AlC 0.5 N 0.5 . The lattice parameters, elastic constants, bulk, shear, Young's moduli, Poisson's ratio and Debye temperature were calculated and compared with those of the end members, Ti 2 AlC and Ti 2 AlN. The temperature dependence of the bulk moduli, thermal expansion coefficient and specific heats of Ti 2 AlC 0.5 N 0.5 were obtained from the quasi-harmonic Debye model. The calculated elastic and thermodynamic properties were compared with experimental data.

Ti 3 SiC 2 –TiC composites with the volume fractions of TiC from 0 to 90% were fabricated by pulse discharge sintering (PDS) technique using Ti–Si–TiC as starting powders in the sintering temperature range of 1250–1400 °C. Phase content and microstructure of the synthesized samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The samples sintered at 1400 °C are almost fully dense for all compositions with relative density higher than 98%. The phase distribution in the synthesized samples is non-uniform. The Vickers hardness increases almost linearly with the volume fraction of TiC up to a value of 20.1 ± 1.4 GPa at 90 vol.% TiC. The flexural strength increases with the volume fraction of TiC to a maximum value of 655 ± 10 MPa at 50 vol.% TiC. The relationship between microstructure and mechanical properties is discussed.

The objective of this study was to analyze gene expression profiles of intervertebral disc samples and peripheral blood mononuclear cells (PBMCs) from patients with degenerative discs using Agilent's Human 1A Oligo microarray. RNA samples from disc tissue and PBMCs were obtained from patients with degenerative discs and from subjects in a control group. RNA samples were reverse-transcribed into Cy5-labeled cRNA, combined with a Cy3-labeled reference and hybridized to oligonucleotide microarrays. Microarrays were scanned by Gene-Pix 4000B and data were analyzed using GenePixPro 3.0 software. The microarray data were validated in the same RNA samples by qRT-PCR analysis of selected genes. For the disc tissue, the mRNA expressions of 522 genes changed obviously in the degeneration group, accounting for approximately 2.64% of all analyzed transcripts. These included transcription-related, ion channel and transport protein, receptor, protein synthesis and modifying, growth factor, etc. For PBMCs, the expressions of 62 genes changed obviously in the patients in the degeneration group. These changes included ion channel, transport protein, transcription-related, DNA synthesis and repair, metalloprotease, immune globulin-related, growth factor-related, extracellular matrix-related, adhesion molecule, etc. Analyzed on the association of the differential expression of genes between disc tissue and PBMCs, some genes were not compatible. The course of intervertebral disc denegation is a complicated dynamic process, however, and may mainly be local pathogenesis. These findings furnish new data for the mechanistic investigation of degenerative discs.

Titanium aluminium carbide (Ti 3 AlC 2 ) displays a unique combination of characteristics of both metals and ceramics coupled with an unusual combination of mechanical, electrical and thermal properties. In this research, the oxidation characteristics of Ti 3 AlC 2 over the temperature range 500–900 °C were studied by synchrotron radiation diffraction (SRD) and secondary-ion mass spectrometry (SIMS) experiments which provided elemental and phase compositional depth profiles over this range. Evidence for the outward diffusion of Al during oxidation was shown for the first time by the complementary SIMS results, which suggested the existence of amorphous Al or aluminium oxide at low temperature oxidation. At 500 °C, only anatase-TiO 2 was detected by SRD in addition to the parent Ti 3 AlC 2 . Transformation of anatase to rutile was observed at 600 °C and was completed by 900 °C. The crystalline phase α-Al 2 O 3 was detected at 900 °C but not at lower temperatures.

Titanium silicon carbide (Ti 3 SiC 2 ) was synthesized by hot-pressing of powder blends of titanium or titanium hydride, silicon and titanium carbide. Commercial titanium powders with two different average particle sizes and titanium hydride powders with six average particle sizes prepared by ball milling were used for the synthesis to investigate their effect on the crystal grain size of synthesized Ti 3 SiC 2 . We found that the grain size of Ti 3 SiC 2 decreases with a decrease in particle size of both titanium and titanium hydride powders. Particularly, employment of titanium hydride powders resulted in finer crystal grains than using titanium powders. We also found that finer titanium hydride powders raise synthetic reaction temperature of Ti 3 SiC 2 and lead to more TiC in the synthesized Ti 3 SiC 2 .

Predominantly single-phase and nearly dense (Cr1−xVx)2AlC (x = 0, 0.1, 0.25 and 0.5) solid solutions were synthesized by pulse discharge sintering (PDS) using Cr, V, Al and C powders as starting materials. Average grain sizes of the V-containing compounds were measured to be the same, around 9 μm. The Vickers hardness of the compounds increases linearly with V content due to solid solution hardening. Thermal conductivity decreases slightly to a minimum value followed by an increase with V content, which is attributed to the phonon and carrier scattering due to the V solution in the C2AlC compound.

We have investigated the bonding properties and bulk modulus of M4AlC3 (M = V, Nb, and Ta) by first-principles calculations. The calculated cohesive energy indicates the enhancement of bond strength of M4AlC3 as V is replaced by Nb and subsequently by Ta. This conclusion was further confirmed by the analysis of density of states of M4AlC3. The bulk modulus of M4AlC3 is found to be proportional to its corresponding binary compound MC. The hardness of M4AlC3 was discussed based on the relationship between the bulk modulus and hardness. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The compressive properties of ternary compound Cr2AlC at different temperatures and strain rates were studied. When tested at a strain rate of 5.6 × 10−4 s−1, the compressive strength decreases continuously from 997 ± 29 MPa at room temperature to 523 ± 7 MPa at 900 °C. The ductile-to-brittle transition temperature is measured to be in the range of 700 to 800 °C. When tested in the strain rate range of 5.6 × 10−5 to 5.6 × 10−3 s−1, Cr2AlC fails in a brittle mode at room temperature, whereas the deformation mode changes from a brittle to a ductile as the strain rate is lower than 5.6 × 10−4 s−1 when compressed at 800 °C. The compressive strength increases slightly with increasing strain rate at room temperature and it is less dependent on strain rate when tested at 800 °C. The plastic deformation mechanism of Cr2AlC was discussed in terms of dislocation-related activities, such as kink band formation, delamination, decohesion of grain boundary, and microcrack formation.

Ternary compound Ti 3 AlC 2 was synthesized through pulse discharge sintering (PDS) the powder mixture of TiH 2 /Al/C without preliminary dehydrogenation. The synthesis mechanism of Ti 3 AlC 2 was revealed to be completed via the reactions among the intermediate phases of Ti 3 Al, TiAl 3 , TiAl, TiC and Ti 2 AlC, as well as the starting reactants. In comparison with the materials synthesized from TiH 2 /Al/TiC or Ti/Al/C powder mixtures, more impurity phases were found in the synthesized Ti 3 AlC 2 . Analysis of the sintering curves as well as the intermediate phase formation during the reactive sintering process revealed that incomplete dehydrogenation of TiH 2 postponed the formation of intermediate phases, which in turn resulted in final products with more impurity phases.

Aluminum nitride (AlN) ceramics are indispensable to semiconductor manufacturing processes because of their high thermal conductivities, high corrosion-resistance to halogen gases and plasmas, high strengths and etc. Titanium aluminum nitride (Ti2AlN) is a ceramic showing high electrical conductivity and machinability. A Ti-Al-N ternary equilibrium diagram indicates a two-phase equilibrium region between Ti2AlN and AlN, which motivated the synthesis of AlN-Ti2AlN composites with added electrical conductivity and machinability to AlN ceramics in a wide temperature range. In this study, an approach to the synthesis of AlN-Ti2AlN composites was made by reactive hot-pressing of Ti/Al/TiN/AlN and Ti/AlN powder mixtures, respectively. Before synthesizing the composites, synthesis of single-phase Ti2AlN has been pursued and almost single-phase Ti2AlN was successfully obtained by the reactive hot-pressing of a Ti/Al/TiN powder mixture with a molar ratio of Ti:Al:TiN=1:1:1 and a Ti/AlN powder mixture with the ratio of Ti:AlN=2:1, respectively. However, all attempts to synthesize AlN-Ti2AlN composites by the reactive hot-pressing of a Ti/Al/TiN/AlN powder mixture with the ratio of Ti:Al:TiN:AlN=1:1:1:9 or a Ti/AlN mixture with the ratio of Ti:AlN=1:1 did not succeed, and the cause of these results are discussed.

First-principles calculations of the thermodynamic properties of Ti2AlC and Ti2SC were carried out. The temperature dependence of bulk modulus, the pressure dependence of normalized volume V=V0, thermal expansion coefficient, specific heats, and Debye temperature were successfully obtained through the quasi-harmonic Debye model in the temperature range from 0 to 1000 K and the pressure range from 0 to 50 GPa. The calculated results were compared with available experimental data. The effects of the bonding strength of Ti-S and Ti-Al on the thermodynamic properties were discussed. [doi:10.2320/matertrans.MAW200903]

The reaction process of ternary compound Cr 2 AlC synthesis was studied. Powder mixture of Cr, Al 4 C 3 and graphite at the composition of Cr:Al:C = 2:1.1:1 was processed by pulse discharge sintering in vacuum in the temperature range of 850 to 1350 °C. The synthesized materials were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with an energy dispersive spectrum (EDS) system. It was found that the amount of Cr 2 AlC phase increased significantly in the temperature range of 950 to 1150 °C at the consumption of Cr and Al 4 C 3 as well as an intermediate phase Cr 2 Al. Predominantly single-phase Cr 2 AlC with small amount of Cr 7 C 3 was obtained as the sintering temperature is above 1250 °C. It is presumed that Cr 2 AlC phase is formed near Al 4 C 3 particle by the diffusion of Cr and the reaction of the diffused Cr with Al 4 C 3 .

In the present study, Ti/Si/2TiC/ x Al ( x = 0, 0.05, 0.1, 0.15, and 0.2) powder mixtures were heated in vacuum for synthesis of Ti 3 SiC 2 powder. It was found that Al addition accelerated the synthesis reaction for Ti 3 SiC 2 . When Al of x = 0.2 was added, the synthesis temperature for single-phase Ti 3 SiC 2 was lowered to 1150 °C from 1500 °C. The mechanism of the accelerating effect of Al addition on Ti 3 SiC 2 formation was revealed to be that molten Al plays the role of deoxidation agent, which prompts the synthesis of Ti 3 SiC 2 through accelerating the formation of Ti 5 Si 3 intermediate phase. In addition, equations for quantitative evaluation of the contents of three coexisting phases (Ti 3 SiC 2 , Ti 5 Si 3 , and TiC) during the synthesis process were derived in this study based on experimental calibration.

Elastic properties of Ta4AlC3 were studied by first-principles calculations. The five independent elastic constants were derived yielding c 11 = 437 GPa , c 12 = 158 GPa , c 13 = 197 GPa , c 33 = 416 GPa , c 44 = 165 GPa . The bulk modulus B , Young’s modulus E , shear modulus G , and Poisson’s ratio v were determined to be 266 GPa, 362 GPa, 142 GPa, and 0.27, respectively. Ta4AlC3 is elastically stable with a Ti4AlN3-like structure. Ta4AlC3 exhibits largely isotropic properties in compression and is slightly anisotropic in shear. The in-plane elastic anisotropy in a – c plane of Ta4AlC3 was also revealed.

We have performed first-principles study on electronic structure and elastic properties of Ti 2 SC. The absence of band gap at the Fermi level and the finite value of the density of states at the Fermi energy reveal the metallic behavior of this compound. The five independent elastic constants were derived and the bulk modulus, Young's modulus, shear modulus, and Poisson's ratio were determined. The high bulk modulus and hardness was found to be originated from the strong Ti 3 d –S 2 p hybridization. Such strong M A bonding is unusual in the MAX phases studied so far. Ti 2 SC is elastically stable and exhibits highly elastic isotropy.

Powders of Ti, Al and TiC were mixed as starting materials for the synthesis of ternary compound Ti 3 AlC 2 at 1200–1400 °C by using pulse discharge sintering (PDS) technique. The fully dense and almost single-phase polycrystalline Ti 3 AlC 2 was obtained at 1300 °C for 15 min, when the molar ratio of the starting powder mixture was selected to be Ti:Al:TiC = 2:2:3. The typical microstructure of Ti 3 AlC 2 was found to consist of plate-like grains with size of about 3–5 μm in width and 20–50 μm in length. The intermediate phases of Ti 3 Al, TiAl and Ti 2 AlC were found during the reactive sintering process and the reactions for the Ti 3 AlC 2 phase formation were proposed.

Ternary compound Ti 3 SiC 2 was rapidly synthesized by pulse discharge sintering the powder mixture of 1TiH 2 /1Si/1.8TiC without preliminary dehydrogenation. Almost single-phase dense Ti 3 SiC 2 was synthesized at 1400 °C for 20 min. The grain size of synthesized Ti 3 SiC 2 strongly depends on sintering temperature. The synthesis mechanism of Ti 3 SiC 2 was revealed to be completed via the reactions among the intermediate phases of Ti 5 Si 3 , TiSi 2 and the other reactants in the starting powder. The Ti–Si liquid reaction occurring above the Ti–Ti 5 Si 3 eutectic temperature at 1330 °C was found to assist the synthesis reaction and densification of Ti 3 SiC 2 . The dehydrogenation of TiH 2 was accelerated by the synthesis reactions.

The electronic structure and phase stability of Ta4AlC3 with α and β polymorphs are studied by first-principles calculations. The calculated formation energies are −0.649 and −0.576 eV/atom for the α and β polymorphs respectively, which means that both of them are thermodynamically stable phases. The total energy of α - Ta4AlC3 is about 0.0866 Ry lower than that of β - Ta4AlC3, indicating that the α polymorph is more stable. The strong hybridization between Ta1 5d and C1 2p, Ta2 5d and Al 3p in α - Ta4AlC3 results in strong interactions between Ta1–C1 and Ta2–Al atoms, which stabilizes the α polymorph of Ta4AlC3.

TiC-Ti 3 SiC 2 composites having the microstructure of fine Ti 3 SiC 2 grains dispersed in TiC matrix were synthesized by two processes, that is, mechanical alloying of a powder blend of Ti, Si and C followed by hot-pressing (MA-HP process) and hot-pressing of a powder blend of Ti, Si and TiC (MIX-HP process). The microstructure, damage tolerance and 4-point flexural strength of the composites were investigated. It was found that more uniform dispersion of Ti 3 SiC 2 grains in TiC matrix was achieved by MA-HP process than by MIX-HP process, while the flexural strength of the composites synthesized by MA-HP process was lower than that by MIX-HP process, which may be attributed to micropores formed in the composites synthesized by MA-HP process. Preferential orientation of Ti 3 SiC 2 (001) and TiC(111) occurred in the composites synthesized by MA-HP process. We proposed two mechanisms of the preferential orientation. We also found that the dispersion of Ti 3 SiC 2 in TiC matrix is effective in improving the damage tolerance of the brittle TiC, evidenced by the fact that no cracks emanated from the comers of Vickers indentations at a load of 9.8 N.

The traditional view that the etiology of lumbar disc herniation is primarily due to age, gender, occupation, smoking and exposure to vehicular vibration dominated much of the last century. Recent research indicates that heredity may be largely responsible for the degeneration as well as herniation of intervertebral discs. Since 1998, genetic influences have been confirmed by the identification of several genes forms associated with disc degeneration. These researches are paving the way for a better understanding of the biologic mechanisms. Now, many researchers unanimously agree that lumbar disc herniation appears to be similar to other complex diseases, whose etiology has both environmental and hereditary influence, each with a part of contribution and relative risk. Then addressing the etiological of lumbar disc herniation, it is important to integrate heredity with the environment factors. For the purpose of this review, we have limited our discussion to several susceptibility genes associated with disc degeneration.

Synthesis of Ti 3 SiC 2 powder was carried out by heat treating powder mixtures of Si, TiC and coarse Ti (−150 μm) in a temperature range of 1000–1400 °C. The phase content of Ti 3 SiC 2 in the synthesized powder was improved to 99% when heat treated at 1400 °C for 4 h. Ti–Si liquid reaction was found to occur above the binary eutectic temperature, and this liquid reaction is believed to have assisted the synthesis reaction of Ti 3 SiC 2 .

Ti3AlC2 was rapidly synthesized by pulse discharge sintering Ti/Al/C (molar ratio 3:1.1:1.8) powder mixtures in a temperature range of 1200–1400 °C. The fully dense and single-phase Ti3AlC2 was obtained at sintering temperature 1250–1350 °C for 15 min and at 1300 °C for 15–60 min. The typical microstructure of polycrystalline bulk Ti3AlC2 consists of plate-like grains, and the grain size can be adjusted by choosing sintering temperature and time. The intermediate phases of AlTi3, AlTi, Ti3AlC and Ti2AlC were found during the reactive sintering process and the mechanisms for the Ti3AlC2 phase formation were proposed.

The traditional view that the etiology of lumbar disc herniation is primarily due to age, gender, occupation, smoking and exposure to vehicular vibration dominated much of the last century. Recent research indicates that heredity may be largely responsible for the degeneration as well as herniation of intervertebral discs. Since 1998, genetic influences have been confirmed by the identification of several genes forms associated with disc degeneration. These researches are paving the way for a better understanding of the biologic mechanisms. Now, many researchers unanimously agree that lumbar disc herniation appears to be similar to other complex diseases, whose etiology has both environmental and hereditary influence, each with a part of contribution and relative risk. Then addressing the etiological of lumbar disc herniation, it is important to integrate heredity with the environment factors. For the purpose of this review, we have limited our discussion to several susceptibility genes associated with disc degeneration.

A powder blend of Ti, SiC and C at a molar ratio of Ti:SiC:C = 3:1:1 was compacted into cylinder and sintered in vacuum for the synthesis of Ti3SiC2. The microstructure of synthesized Ti3SiC2 showed unique morphology. Variation in phase and microstructural morphology with temperature during sintering was investigated by X-ray diffraction analysis and a scanning electron microscope equipped with an energy dispersive X-ray analyzer in order to elucidate reaction mechanism. Two kinds of powder blends, Ti/Si and Ti/C, were also compacted and sintered to confirm the effect of diffusion of Si and C atoms into Ti particles on the morphological change of Ti particles. As a result, we proposed the progress of synthesis as follows: (1) Si and C atoms start to diffuse into Ti particles from SiC and C particles over 1023 K, (2) the diffusion of Si and C atoms is enhanced rapidly over α/β phase transition temperature of Ti, which results in the formation of shell structure having ruffled surface composed of Ti5Si3 and TiC on Ti particle surfaces, (3) the shell grows and joins together with neighbor ones and pure Ti core in Ti particles reduces in size, (4) Ti3SiC2 is formed by the reaction of Ti5Si3 with TiC over 1623 K, (5) finally, Ti3SiC2 with TiC is synthesized over 1823 K. The joined shell structure having ruffled surface formed during sintering remained after the formation of Ti3SiC2, which resulted in the formation of the unique morphology.

Single-phase, nearly fully dense ternary compound Ti 3 SiC 2 was successfully synthesized by pulse discharge sintering (PDS) Ti/Si/TiC powder mixture, where coarse Ti powder (−0.15 mm) was used, at 1350–1400 °C for a short time of 20 min. Ti 3 SiC 2 was found to form through reaction among intermediate phases of Ti 5 Si 3 , TiSi 2 and the starting powders. Evidence of Ti–Si liquid reaction above Ti–Ti 5 Si 3 eutectic temperature was revealed by studying the shrinkage displacement curve, and this liquid reaction is believed to have greatly assisted the ternary phase synthesis reaction as well as densification.

In this paper we report on a detailed statistics-based study of the effect of various environments – air, argon, vacuum, oil and water – on the room temperature spontaneous nucleation and growth of lead whiskers from hacksaw-cut surfaces of three leaded commercial brasses. The samples were initially held in the various environments for 166 h, before being stored in ambient air for a total of 1126 h. The environment was found to have a strong effect. The highest whisker density, ∼30,000 cm −2 , was observed for the sample initially kept under a mechanical (∼1 Pa) vacuum; the lowest, ∼3000 cm −2 , was observed for the sample initially immersed in water; the densities of the others were in between. The samples held in water only grew whiskers when removed from the water. Once exposed to air, a few whiskers grew at an average rate that, at 0.9 nm s −1 , was the highest measured. When the samples were exposed to air, after the initial storage in the different environments, both nucleation and growth of the whiskers were accelerated, before ultimately ceasing to grow roughly 400 h after creating the surfaces from which the whiskers grew. These results are consistent with a scenario in which oxygen and/or moisture diffusion down the Pb/brass interfaces results in a volume expansion that provides the driving force for whisker growth. The results also indicate that the oxygen levels needed for whisker growth can be as low as a few parts per million.

Single-phase dense Ti3AlC2 was rapidly synthesized through pulse discharge sintering a TiH2/Al/TiC powder mixture. Dehydrogenation of TiH2 was rapidly accomplished during the synthesis process at the heating up stage below 800 °C. The formation of Ti3AlC2 was found to be achieved by the reactions among the intermediate phases of AlTi3, Al3Ti, AlTi and Ti2AlC, as well as the reactants in the starting powders.

Ti3SiC2–TiC binary-phase material was investigated with the aim of developing a new hard product. The starting material for the synthesis was prepared by compounding raw powders of Ti, Si and TiC at molar ratios of 1:1:x (x ¼ 1:8{7:0). The products were synthesized by sintering and the structures of the samples produced were examined. The product obtained was single-phase Ti3SiC2 when x was 2.0 or less and a Ti3SiC2–TiC binary-phase structure when x was more than 2.0. The mass fraction of TiC in the binary-phase structure increased with increasing x. The optimum sintering temperatures for densification were different for the different synthesized structures: the Ti3SiC2 single-phase structure was well densified at up to 1673 K, whereas higher temperature was required to dinsify the Ti3SiC2–TiC binary-phase structure. These results suggest the possibility of producing Ti3SiC2–TiC functionally graded materials. The traveling-zone sintering method permits integrated sintering of materials at variable temperatures. Powder mixtures with TiC contents from 1.8 to 7.0 mole were layered in the same mold and sintered at variable temperatures from 1643 to 1733 K. The synthesized structure was successfully graded, as in the case of individual synthesis of each of the compounds. The hardness of the produced sample showed a tendency to increase with increasing mass fraction of TiC. These results prove that the traveling-zone sintering method has the potential to fabricate functionally graded materials that require variable sintering temperatures. [doi:10.2320/matertrans.48.139]

Ternary compound Ti 3 SiC 2 was successfully synthesized by pulse discharge sintering the powder mixture of TiH 2 /SiC/C. When the molar ratio of the starting powder mixture was selected to be TiH 2 SiC : C = 2.8 : 1 : 0.8, single-phase dense Ti 3 SiC 2 was synthesized at 1400°C for 20 min. The grain size of synthesized Ti 3 SiC 2 strongly depends on the sintering temperature. The synthesis mechanism of Ti 3 SiC 2 was revealed to be completed via the reactions among the intermediate phases of Ti 5 Si 3 C x and TiC. It is found that dehydrogenation was accelerated by the synthesis reaction during sintering progress. Compared with Ti/SiC/C powder mixture, the TiH 2 /SiC/C mixed powder is favorable for synthesizing Ti 3 SiC 2 through PDS technique.

Strengthening of titanium silicon carbide (Ti 3 SiC 2 ) was investigated by the grain orientation control and silicon carbide (SiC) whisker dispersion. Ti 3 SiC 2 with preferentially oriented grains was prepared by hot-pressing of milled Ti 3 SiC 2 powder. Composites were also fabricated by hot-pressing of a blend of the milled Ti 3 SiC 2 powder and SiC whiskers. During hot-pressing, the preferential orientation of Ti 3 SiC 2 grains was achieved while the precipitation of titanium carbide (TiC) occurred. As a result, 4-point bending strength of preferentially-oriented Ti 3 SiC 2 was approximately 1.5 times the randomly-oriented pure Ti 3 SiC 2 in a temperature range from room temperature to 1073 K. The bending strength of Ti 3 SiC 2 with 15 vol% whiskers reached approximately 1 GPa, approximately 3 times the randomly-oriented pure Ti 3 SiC 2 , in the range to 1073 K. The results in this study indicate that the strengthening effect on Ti 3 SiC 2 was contributed from the orientation control, TiC precipitation and SiC whisker dispersion.

Almost single-phase ternary compound Ti3AlC2 was successfully synthesized by pulse discharge sintering (PDS) from Ti/Al/TiC powder mixtures with molar ratio of 2:2:3 . The typical microstructure of Ti3AlC2 was found to consist of plate-like grains with mean size of 9.5 mm in length. Four-point bending testing results revealed that the fracture behavior is brittle below 1200 � C, and some characteristics of plastic deformation were observed at higher testing temperatures. The polycrystalline Ti3AlC2 synthesized by PDS technique shows good strength at high temperatures. [doi:10.2320/matertrans.MAW200703]

Ti 3 SiC 2 bulk materials were synthesized from the starting powders of 1Ti/1Si/2TiC– x Al and 3Ti/1SiC/1C– x Al (molar ratios, x ranges from 0.05 to 0.15) at temperatures between 1100 and 1400 °C for 15 min by pulse discharge sintering technique. X-ray diffraction and scanning electron microscopy were used to characterize the synthesized materials. It was found that the addition of Al decreases the content of TiC in the sintered samples and expands the optimal temperature range for the synthesis of Ti 3 SiC 2 bulk materials. By addition of Al, Ti 3 SiC 2 bulk materials of high phase-purity have been synthesized at 1100 and 1200 °C from 1Ti/1Si/2TiC and 3Ti/1SiC/1C starting powders, respectively.

Epidural fibrosis might occur after lumbar discectomy and contributes to failed back syndrome. Transforming growth factor (TGF)-β has been reported to influence multiple organ fibrosis, in which connective tissue growth factor/cysteine-rich 61/nephroblastoma overexpressed 2 (CCN2) and CCN5 are involved. However, the effect of CCN2 and CCN5 on TGF-β induced fibrosis has not yet been elucidated. This study reports that CCN2 and CCN5 play opposing roles in cell proliferation and transdifferentiation of human skin fibroblasts or rabbit epidural scar-derived fibroblasts exposed to TGF-β. We observed that TGF-β1 induced fibroblasts proliferation and differentiation in a dose-dependent manner (from 0 μg/L to 20 μg/L). Meanwhile, CCN2 expression is up-regulated while CCN5 expression is inhibited by TGF-β1 exposure. Furthermore, it is demonstrated that CCN2 overexpression leads to promoted proliferation and elevated collagen and α-smooth muscle actin (α-SMA) expression, which are inhibited by CCN5 overexpression. Moreover, it is shown that the cysteine knot (CT) domain, present in CCN2 but absent in CCN5, plays an essential part in fibroblast proliferation and differentiation. Additionally, enhanced TGF-β and CCN2 expression but decreased CCN5 expression is found in rabbit epidural scar-derived fibroblasts. Overall, the results show the opposing effects of CCN2 and CCN5 on fibroblast proliferation and transdifferentiation induced by TGF-β.

In our previous study, we reported that heparan sulfate 6-O-sulfotransferase‑2 (HS6ST2) plays an important role in the cartilage of patients with osteoarthritis and Kashin-Beck disease and that it regulates aggrecan (Acan) metabolism and the viability of chondrocytes. However, its role in chondrocyte differentiation remains poorly understood. In the present study, we aimed to investigate the role of HS6ST2 in chondrocyte differentiation in vitro using mouse prechondrocytic cells. We found that the overexpression or silencing of HS6ST2 significantly enhanced or abrogated the effects of fibroblast growth factor (FGF)‑2 on chondrocyte growth, respectively. We found that the overexpression of HS6ST2 significantly induced the expression of Acan as well as the amount of total proteoglycans in the prechondrocytic cells in the presence of FGF‑2, whereas the silencing of HS6ST2 caused the opposite effect. Furthermore, the expresssion of FGF‑2‑induced sex‑determining region Y‑type high mobility group box protein 9 (SOX9), a major transcription factor for chondrocyte proliferation and differentiation, was also enhanced or blocked by HS6ST2 overexpression or HS6ST2 knockdown, respectively. Additionally, Wnt/β‑catenin signaling, which inhibited chondrocyte proliferation and differentiation, was suppressed by HS6ST2. Taken together, these data suggest that HS6ST2 plays an important role in regulating chondrocyte growth and differentiation by modulating FGF‑2 signaling, thus indicating that it may be a potential and valuable molecular target for the treatment of skeletal dysplasias, such as dwarfism.

During pressureless reactive sintering of Ti3SiC2 we found that adding small amounts of Al (∼0.68 wt.%) to the powder mixture of Ti/Si/2TiC improves the density of the compact by 38%, and enhances the formation of the desired phase, Ti3SiC2. Further increase in the Al content—up to 2.7 wt.%—did not show enhanced effect. The mechanism is believed to be the deoxidation of the starting powders by the molten Al.

Titanium silicon carbide Ti3SiC2 was synthesized from a powder blend of Ti, Si and TiC at a molar ratio of Ti:Si:TiC = 2:2:3. The powder blend was pressed and shaped into a cylinder and then sintered at various temperatures in vacuum. X-ray diffraction analysis was conducted on the cylinders sintered at various temperatures. Results of the XRD analysis revealed that Ti5Si3, the most thermodynamically stable phase in Ti–Si system, was preferentially formed by the reaction between Ti and Si powders followed by the formation of TiSi2 from remaining Ti and Si powders in a relatively low temperature range. These silicides reacted with TiC to form Ti3SiC2 at higher temperatures. The final phases in the cylinders sintered at temperatures over 1729 K were Ti3SiC2 and Ti5Si3, which well agrees with those estimated by a Ti–Si–C phase diagram. On the other hand, final phases in disks sintered under pressures of 14 MPa or more by using a carbon mold were found to be Ti3SiC2 and TiC, which suggests the equilibrium changes with the pressure.