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Composite photocatalyst, MWNTs/TiO2, is prepared using sol-gel method and dried through microwave irradiation. Characterization of the composite shows that, with the increase of microwave power till 400 W, the average diameter of MWNTs/TiO2 composite reduces gradually, and better dispersion of the composites is also acquired at the microwave power of 400 W. However, a further increase of the power results in the average diameter of the composite enlarged, and more aggregative composites are obtained. Furthermore, photodegradation of 1,2,3-trichlorobenzene (1,2,3-TCB) with the composite photocatalysts of MWNTs/TiO2 induced under different microwave conditions is studied. It is found that the photodegradation of 1,2,3-TCB follows the first-order kinetics. The microwaving conditions for producing the composite photocatalysts with the highest photocatalytic activity are further determined as 5 min irradiation at 400 W. Under such conditions, the rate constant of 1,2,3-TCB photodegradation is 0.023 7 min(-1) which is elevated by 52% comparing to those obtained using non-microwaved composites.

Effects and kinetics of photocatalytic degradation of 1,2,4-trichlorobenzene with composite photocatalysts of TiO2 coated on carbon nanotubes and nano-TiO2 photocatalysts were studied, respectively. It was found that the composite photocatalysts was better than the nano-TiO2 for photocatalytic degradation of 1,2,4-trichlorobenzene. After 60 min UV irradiation at 254 nm, there was 70% of the initial 1,2,4-trichlorobenzene degraded with the composite photocatalyst while only 51% of the initial 1,2,4-trichlorobenzene degraded with the nano-TiO2. Results of photocatalytic degradation kinetics also proved that the 1,2,4-trichlorobenzene degradation rate constant with the composite photocatalyst was 0.019 6 h(-1), which was increased by 63.3% compared to that with nano-TiO2. According to molecular structure theory, analysis of dissociation energy of C--Cl bond of chlorobenzenes predicated that main pathway of photocatalytic degradation of 1,2,4-trichlorobenzene followed that its ortho-Cl could be took off first to form 1, 4-dichlorobenzene, and it might be further dechlorized and finally be mineralized. The first step of photodechlorination for 1,2,4-trichlorobenzene was also experimentally confirmed through identified 1,4-dichlorobenzene as its product.

Ti and its alloys have a variety of applications in aerospace industry and medical implants. The formation of hydride has been used in biomedical areas and can significantly influence the mechanical performance of materials. In this work, we investigate the orientation dependence of hydride precipitation in commercially pure titanium via interrupted in-situ electron backscatter diffraction (EBSD) measurements. The results reveal that hydrides during hydrogen charging at room temperature exhibit two types of orientation relationships with α-titanium, i.e., { 0001 } α / / { 1 1 ¯ 1 } δ < 1 2 ¯ 10 > α / / < 110 > δ with interface plane { 10 1 ¯ 3 } α / / { 1 1 ¯ 0 } δ (B-type), and {0001} α //{001} δ < 1 2 ¯ 10 > α / / < 110 > δ with interface plane { 10 1 ¯ 0 } α / / { 1 1 ¯ 0 } δ (P-type). Significant orientation dependence of hydride precipitation is observed, especially when { 10 1 ¯ 3 } , { 10 1 ¯ 0 } , {0001} or { 11 2 ¯ 0 } planes of the parent grains are parallel to the diffusion surface. The displacement gradient tensor based accommodation shows that the orientation dependence is attributed to the strain relaxation of hydride transition. Three types of hydride platelets are characterized: parallel hydride platelets (Type I), crossed hydride platelets (Type II) and clustered hydride platelets (Type III). The multiple morphologies of hydride platelets resulting from the hydride variant selection and interaction are dependent on the crystal orientation of the matrix. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract Shock loading causes complicated twinning processes in Ti and Ti alloys. In this work, two types of {10 1 ¯ 2} sequential twinning processes are for the first time reported according to electron backscatter diffraction (EBSD) characterization of titanium sheets that are subjected to shock loading. One is described as {11 2 ¯ 1} ⇒ P → {10 1 ¯ 2} ( T i I I ⇒ P → T j I ), i.e., {10 1 ¯ 2} sequential twinning is activated in the parent grain (P) along with {11 2 ¯ 1} twins. The other is described as {11 2 ¯ 2} ⇒ {11 2 ¯ 4} → {10 1 ¯ 2} ( C i I ⇒ C j I I → T k I ), i.e., {10 1 ¯ 2} secondary twinning is stimulated inside {11 2 ¯ 4} twin by co-zone {11 2 ¯ 2} twin. A statistical analysis according to EBSD characterization reveals the well-defined crystallographic relations between sequential {10 1 ¯ 2} twin variants and the primary/incoming twins, i.e., T i I I ⇒ P → T i I o r T i + 1 I and C i I ⇒ C i + 3 I I → T i I or T i + 1 I . We proposed and examined two sequential twinning mechanisms, (i) emissary twinning disconnections at steps along twin boundary for the first case and (ii) shear transformation into the primary twin for the second case, based on dislocation theory and the deformation accommodation ability of the sequential {10 1 ¯ 2} twinning to the shear deformation of the primary/incoming twin. Crystal plasticity modelling is performed to calculate the local stress field associated with the proposed twinning mechanisms. The results demonstrate that the preferred twin variant observed in experiments has the maximum resolved shear stress among the six twin variants. Our work suggests that complicated twinning processes under shock loading obey crystallographic relations according to deformation accommodation ability. The findings from this study can be implemented into meso-/macro-scale crystal plasticity models for predicting mechanical behaviors and texture evolution of polycrystalline aggregates of hexagonal materials. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract { 11 2 ¯ 2 } twinning commonly takes place in α-titanium (α-Ti). High-resolution transmission electron microscopies (HRTEM) explored various steps along { 11 2 ¯ 2 } coherent twin boundary. Topological model of { 11 2 ¯ 2 } twin revealed twinning disconnections (TDs) that are represented by ( b i , i h { 11 2 ¯ 2 } ) corresponding to a step height i h { 11 2 ¯ 2 } and a shear vector b i. Atomistic simulations were conducted to study the energies and kinetics of TDs. Combining microscopies and atomistic simulations, we concluded that ( b 3 , 3 h { 11 2 ¯ 2 } ) is the elementary TD and ( b 1 , h { 11 2 ¯ 2 } ) is the reassembly TD. Steps observed in HRTEM thus can be treated as a reassembly of ( b 3 , 3 h { 11 2 ¯ 2 } ) TDs and ( b 1 , h { 11 2 ¯ 2 } ) TDs. In addition, Electron Backscatter Diffraction (EBSD) maps revealed { 11 2 ¯ 2 } → { 11 2 ¯ 1 } double twins in α-Ti. Using two-dimensional and three-dimensional atomistic simulations, we demonstrated the nucleation of ( b 1 , h { 11 2 ¯ 2 } ) TD and { 11 2 ¯ 2 } → { 11 2 ¯ 1 } double twin through the interaction between basal < a > dislocation and { 11 2 ¯ 2 } twin. Our results enrich the understanding of { 11 2 ¯ 2 } twinning including TDs, steps, and { 11 2 ¯ 1 } secondary twins in hexagonal metals. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract Six twinning modes have been reported in α-titanium, including three extension twinning modes {10 1 ¯ 2}, {11 2 ¯ 1} and {11 2 ¯ 3} and three compression twinning modes {11 2 ¯ 2}, {11 2 ¯ 4} and {10 1 ¯ 1}. {10 1 ¯ 2} and {11 2 ¯ 2} twins are frequently observed without strong dependence on strain rate, while {11 2 ¯ 1} and {11 2 ¯ 4} twins are observed at high strain rate. These twinning modes and their interactions such as double twinning play significant roles in determining mechanical properties and texture evolution of α-titanium. In this work, we study double twinning associated with {11 2 ¯ 1} primary twin. In order to activate {11 2 ¯ 1} twinning, a split Hopkinson pressure bar (SHPB) device was adopted to conduct high strain rate (∼2600 s−1) compression of high purity titanium along the extrusion direction. We observed 453 {11 2 ¯ 1}→{11 2 ¯ 2} double twins but zero {11 2 ¯ 1}→{11 2 ¯ 4} double twins in six grains. Crystallographic analysis enables the classification of {11 2 ¯ 1}→{11 2 ¯ 2} double twins into Group I (29.5° < 1 ¯ 100>), Group II (55°<5 5 10 ¯ 3>), Group III (80.6°<1 1 ¯ 00>) and Group IV(86.8°< 5 ¯ 15 10 ¯ 3>) according to the misorientation angle and axis pair. Groups I and II dominate in the proportion of experimentally detected double twins while Groups III and IV take a small proportion. We account for these phenomena according to apparent Schmid factor, modified deformation gradient accommodation, and twin nucleation via dislocation dissociation. The results demonstrate that the preferred secondary twinning mode and corresponding variant would, to the greatest extent, relax plastic deformation associated with the primary twinning. Graphical abstract Image 1 Highlights • High strain rate compression was conducted for high purity titanium along the extrusion direction. • EBSD reveals plenty of {11 2 ¯ 1}-{11 2 ¯ 2} double twins but zero {11 2 ¯ 1}-{11 2 ¯ 4} double twins. • {11 2 ¯ 1}-{11 2 ¯ 2} double twins are classified into four groups. Groups I and II prevail over Groups III and IV. • The preferred secondary twin mode and corresponding variant would maximally relax plastic deformation by the primary twinning. [ABSTRACT FROM AUTHOR]

We experimentally characterized four types of double twins in pure titanium and discussed the selection of secondary twin variants based on the apparent Schmid factor (a-SF), the displacement gradient accommodation (DGA), the modified DGA (m-DGA), and the nucleation via dislocation dissociation (NDD). The four types of double twins are classified into two families according to their zone axes: co-family double twins and non-family double twins. Co-family double twins share the zone axis <10 1 ¯ 0>. Non-family double twins have different zone axes with one along < 11 2 ¯ 0 > and the other along <10 1 ¯ 0>. Experimental observations reveal that the co-family double twins have one secondary twin variant prevailed over others and the non-family double twins have two secondary twin variants preferred than others. The a-SFs associated with secondary twins are always positive once the primary twin is activated, thus predicting no obvious preference for the selection of secondary twin variants. The m-DGA and NDD correctly predict the selection of secondary twin variants, implying that the preferred secondary twin variant would, to the greatest extent, relax plastic deformation associated with the primary twinning and the nucleation of the secondary twin variant is facilitated by the accumulation of available gliding dislocations at the primary twin boundary. [ABSTRACT FROM AUTHOR]

contraction twins that are commonly activated in α-titanium interact to each other and form three types of twin-twin junctions (, , TTJs) corresponding to the crystallography of six twin variants (i = 1,2, …, 6). We detected 243 TTJs in rolled pure α-titanium sheets. Electron backscatter diffraction analysis reveals that TTJs are profuse, 79.8% among three types while and TTJs take up 17.7 and 2.5%. Twin transmission does not occur. Consequently, boundaries associated with twin-twin interactions block twin propagation and influence twin growth. We explain structural features of TTJs according to the Schmid factor analysis and the reaction mechanism of twinning dislocations. The knowledge regarding TTJs provides insight for improving the predictive capability of meso/macro-scale crystal plasticity models for hexagonal metals. [ABSTRACT FROM AUTHOR]

We experimentally studied sequential { 10 1 ¯ 2 } twinning in rolled pure titanium at room temperature and identified a new sequential twinning mechanism, i.e., { 10 1 ¯ 2 } ( T i I ) extension twin stimulated by the twin-twin junction of two primary {11 2 ¯ 1 } extension twins T i − 1 II and T i II , which holds a certain relation T i − 1 II T i II → T i I . Schmid factor analysis, as the local stress is taken into account, is able to determine the position of sequential twin variant, but cannot determine the twin variant. Displacement gradient accommodation is used to determine the twin variant. The well-known secondary {10 1 ¯ 2} ( T j I ) extension twins in primary {11 2 ¯ 2} ( C i I ) contraction twins (referred to as C i I → T j I double twinning) are also analyzed according to a generalized Schmid factor analysis. Displacement gradient accommodation and twin nucleation based on dislocations dissociation only work well for the most active twin variants, but cannot address other phenomena associated with C i I → T j I double twinning. For rarely activated twin variants, displacement gradient accommodation was not satisfied. [ABSTRACT FROM AUTHOR]

By compression along the normal direction of rolled pure titanium sheet, primary { 11 2 ¯ 2 } type compression twins were observed, followed by secondary { 10 1 ¯ 2 } extension twins. The latter can be classified into three groups according to their misorientation with respect to the parent matrix grains: 41.34° around < 5 143 ¯ > (Group I), 48.44° around < 5 ¯ 50 3 ¯ > (Group II), and 87.85° around < 7 43 ¯ 0 > (Group III). The experimental observations revealed the following activity frequency of these groups: Group II is the most frequent followed by Group I, and only a few secondary twins can be seen for Group III. When the classical Schmid factor (SF) analysis is applied, the smallest activity is predicted for Group III, in agreement with the experimental observations. However, the SF based criterion fails to distinguish between Group I and Group II variants. Similarly, the twin-shear accommodation based variant selection model proposed earlier for titanium [Qin and Jonas, Acta Mater. 75 (2014) 198–211] is not effective because the easiest accommodation by prismatic slips favors Group III variants which are nearly absent in the experiment. A possible explanation can be based on the smallest inclination angle of the secondary twinning habit plane with respect to the primary one, proposed by Barnett et al. [Acta Mater. 56 (2008) 5–15] which clearly favors Group II. It cannot make distinction between variants of the same group but can predict the right variants if complemented with the SF criterion. In the present work a new approach is proposed in order to disclose the preference for Group II variant over Group I. It is based on the special twinning geometry that applies to Group II; the intersection line of the primary and secondary twin planes lies in an active prismatic plane in the primary twin. Consequently, dislocation reactions are possible for the selection of secondary twin variant in Group II. Namely, prismatic < a > type dislocations in the primary twin can produce partial dislocations that activate the corresponding secondary twin variant. Nevertheless, a further selection rule has to be applied to choose one out of the two possible Group II variants; this is based on the higher Schmid factor of the two secondary variants. By contrast, pyramidal dislocations would be required for the formation of Group I twins, which is less likely due to their relatively high critical resolved shear stress. [ABSTRACT FROM AUTHOR]

The intersection of two 10 1 ̅ 2 twins has been extensively reported in hexagonal metals and appears at grain boundaries with low misorientation angles. In the current work, compression was applied along the normal direction of rolled pure titanium. Primary 11 2 ̅ 2 contraction twins accommodated by adjacent 10 1 ̅ 2 extension twins were found at high angle grain boundaries with misorientation angles close to 90°. The mechanism accounting for the variant selection of the adjoined 10 1 ̅ 2 twins is examined in terms of Schmid factor and accommodation capacity of potential twin variants. [ABSTRACT FROM AUTHOR]

Deformation twins are likely nucleated at and impeded by grain boundaries (GBs), developing shear transformation bands. Knowing the accommodated deformation in adjacent grains to the twinning shear is essential for understanding mechanical properties and the evolution of microstructure and texture of polycrystalline aggregates. Based on EBSD analysis, we characterize and statistically group accommodated deformation modes in the neighbor to {11 2 ¯ 2} compression twins (CTWs) in titanium with respect to the misorientation axis/angle. Two types of CTWs are preferably activated in adjacent grains with low misorientation angles, two types of extension twins (ETWs) are favorably activated in adjacent grains with high misorientation angles, and some of {11 2 ¯ 2} CTWs terminate at GBs with high misorientation angles. We discuss the preference of accommodated deformation modes and the selection of twin variants based on the SDGA criterion which couples the displacement gradient accommodation (DGA) and stress driven accommodation (SDA) criteria. Although misorientation angle of GBs is widely used to predict the preferred deformation modes, we demonstrate that misorientation axis that was often ignored, must be considered in determining the preferred deformation modes especially for large misorientation angles. Finally, we predict the misorientation angle/axis pairs with respect to the activity of four twinning modes and two slip systems as the best accommodation mechanism in adjacent grains. The results are useful for the implementation of intergranular deformation mechanisms in multiscale modeling and the design of HCP materials with specific GB characteristics. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, abundant types of deformation twins were introduced in CP-Ti by cryogenic rolling. The stability of the twins under the annealing process and their contribution to texture were investigated. The EBSD results revealed that {11 2 ¯ 2} compression twins as the primary twin result in the texture with c-axis near ND and RD, while {10 1 ¯ 2}and {11 2 ¯ 1} tension twins as the primary twin induce the texture with c-axis nearly parallel to TD. Besides, the asymmetric texture intensity of the as-received sheet will be improved by the reorientation induced by deformation twins during the annealing process. Most twins show good thermal stability during the annealing process at 550 °C, however, all twins rapidly disappeared at 650 °C. The {10 1 ¯ 2} twins are the most thermally stable during annealing treatment at 600 °C. After full recrystallization, the texture induced by matrix reorientation maintains, while the texture associated with primary twins recovers. • Abundant deformation twins are activated in cryogenic rolled CP-Ti. Different twin interactions are investigated. • All twins show good thermal stability at 550℃ while they rapidly disappear at 650℃. {10 1 ¯ 2 } twins show the best thermal stability at 600℃. • The texture components induced by primary twins recover while those by secondary twins maintain after annealing. [ABSTRACT FROM AUTHOR]