Chemical Bond Strength Research Articles

A hybrid process technology of SiC die separation

ABSTRACT Silicon carbide (SiC) is ideal for making powerful, high-frequency chips for 5 G and electric vehicles due to its wide band gap and resistance to high voltage. However, its powerful chemical bond strength and extreme hardness make it difficult for die separation in the post-wafer process. A hybrid process technology is proposed, where die scribing is performed on SiC wafer using a femtosecond pulsed laser-assisted ablation. The extremely short energy pulses forced the ablation of traces of SiC at extreme speed, breaking chemical bonds and thereby reducing strength and hardness for easy high-speed cutting along the scribed lanes with a polycrystalline diamond wheel. The experiment showed that the average stage current dropped from 0.90 A to 0.45 A and kerf chipping ratio from 11.7 to 4.1 during die separation, proving that the process removed materials along the separation lanes using a wheel tool at low grinding force, creating separation lanes of outstanding straightness and minimal kerf chippings and SiC dies of high integrity. Furthermore, thanks to the on-line rotational machining and dressing of the wheel tool, the blunt diamond abrasive cutting edge could be redressed to expose chip pockets of appropriate depth and protruding grinding edges with a favorable negative rake angle. The established grinding regime utilizing a pressure-grinding force in cutting and material removal reduced cracking at the SiC surface. In this paper, the laser energy density, scanning speed, number of ablations, focus position, as well as the speed, feed-rate and grinding depth of the wheel tool are also discussed in detail.

Degradation of atmospheric plasma sprayed Gd4Al2O9 coating attacked by molten Na2SO4+V2O5 salt mixture at 700–950 °C

In this work, investigation on degradation of the APS Gd4Al2O9 as a new coating against the 50 wt% Na2SO4+50 wt% V2O5 molten salt mixture at 700oC–950 °C for 2 h and 10 h has been conducted. Results indicate that the as-sprayed Gd4Al2O9 coating exhibited outstanding corrosion resistances. Factors related to higher Gd3+ cation ratio, Gd2O3 as a stronger basic oxide than Al2O3, Gd–O with larger chemical bond length and lower bond energy were responsible for a rapid formation of a continuous GdVO4 corrosion layer at any temperature level and corrosion duration. Amorphous phase with much reduced chemical bond strengths in the as-sprayed Gd4Al2O9 coating leading to a significantly reduced apparent porosity level but rather increased corrosion reaction speed played an important role in consuming and solidifying the molten salt mixture as fast as possible.

Effect of the Pretreatment on the Properties of Cement-Based Recycled Powder

Three pretreatment methods including calcination, carbonization, and a carbonization-calcination combined pretreatment were studied to understand the pretreatment mechanisms for cement-based recycled powder (CRP). The mineral and microstructure of the CRP sample were investigated through X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermal gravity (TG) analysis, and scanning electron microscopy (SEM) after exposure to different thermal temperatures (400 °C, 600 °C, and 800 °C), carbonization times (6 h, 1 d, and 3 d), and pre-carbonization for 1 d followed by heating at 800 °C. The results showed that the optimal thermal pretreatment temperature was approximately 720–800 °C. Through the process of calcination, the C-S-H, Ca(OH)2, and CaCO3 minerals in the CRP sample underwent decomposition to produce CaO or C2S. During carbonation, the pretreatment not only results in the increased production of CaCO3 owing to the reaction of the C-S-H gel and Ca(OH)2 with CO2, but also enhances its properties and the strength of chemical bond between CaCO3 and the post-hydration products. Both CaCO3 and CaO were present after the combined pretreatment, which indicates that the CaCO3 mineral formed superior stability after it had been pre-carbonated. Due to fewer impurities in CRP, the positive effect of the pretreatment on CRP was significantly better than that on recycled powder derived from construction and demolition waste.

Interactions and reactivity in crystalline intermediates of mechanochemical cyclorhodation reactions.

There is experimental evidence that solid mixtures of the rhodium dimer [Cp*RhCl2]2 and benzo[h] quinoline (BHQ) produce two different polymorphic molecular cocrystals called 4α and 4β under ball milling conditions. The addition of NaOAc to the mixture leads to the formation of the rhodacycle [Cp*Rh-(BHQ)Cl], where the central Rh atom retains its tetracoordinate character. Isolate 4β reacts with NaOAc leading to the same rhodacycle while isolate 4α does not under the same conditions. We show that the puzzling difference in reactivity between the two cocrystals can be traced back to fundamental aspects of the intermolecular interactions between the BHQ and [Cp*RhCl2]2 fragments in the crystalline environment. To support this view, we report a number of descriptors of the nature and strength of chemical bonds and intermolecular interactions in the extended solids and in a cluster model. We calculate formal quantum mechanical descriptors based on electronic structure, electron density, and binding and interaction energies including an energy decomposition analysis. Without exception, all descriptors point to 4β being a transient structure higher in energy than 4α with larger local and global electrophilic and nucleophilic powers, a more favorable spatial and energetic distribution of the frontier orbitals, and a more fragile crystal structure.

Crystal structure, lattice energy and microwave dielectric properties of melilite-type Ba1-xSrxCu2Ge2O7 ceramics

The Ba1-xSrxCu2Ge2O7 was successfully obtained through the solid-state reaction method, with single-phase BaCu2Ge2O7 formed at 850 °C. Scanning electron microscopy analysis revealed the excellent chemical compatibility of Ba1-xSrxCu2Ge2O7 with silver. The properties of Ba1-xSrxCu2Ge2O7 ceramics were explained using the P-V-L theory. The εr-corr decreased with the polarization rate (Σχu*Nbu) and ion polarization of the unit cell. The Q×f increased with the chemical bond strength and lattice energy (Ucal), particularly the lattice energy of the Ge-O bond (U(Ge-O)). The τf exhibited an opposite trend to the Q×f value and was influenced by the U(Cu-O) and susceptibility of the Cu-O bond (χ(Cu-O)). Sintering at 875 °C for 3 h yielded optimal microwave dielectric performance for Ba1-xSrxCu2Ge2O7 ceramics, with observed values of εr = 9.26 ± 0.14, Q×f = 85,660 ± 4200 GHz, and τf = −15.6 ± 1.1 ppm/°C at x = 0.10. These promising microwave dielectric properties make Ba1-xSrxCu2Ge2O7 a potential candidate for LTCC material applications.

Effect of Ni doping on elastic properties, fracture toughness, electronic properties, and thermal conductivity of η'-Cu6Sn5 in Sn-Cu solder: A first-principles calculation

The phase stability, elastic properties, fracture toughness, electronic structure and thermal conductivity of Ni-doped η'-Cu6Sn5 have been obtained using first-principles calculations. Four Cu and three Sn doped sites were taken into account on according to the crystal structure of η'-Cu6Sn5. The results showed that Ni-doped η'-Cu6Sn5 compounds are thermodynamically stable in the ground state. In addition, Ni also favors replacing the Sn sites. The doping of Ni atom increases elastic modulus and elastic anisotropy, and improves the plasticity of the alloy. In addition, the doping of Ni increases both the thermal conductivity and fracture toughness of η'-Cu6Sn5, while the doping of Ni atoms forms strong covalent bonds with neighboring Cu and Sn atoms, which enhances the chemical bond strength.

BITUMEN PLANT WASTEWATER TREATMENT

Wastewater from oil refineries is considered toxic and dangerous to the environment and human health, because their composition is complex, they are capable of forming other compounds, undergoing changes over time, and the constancy of most organic compounds, the strength of chemical bonds, undoubtedly complicate their biological and chemical oxidation and decomposition. Treatment plants consist of stages of mechanical, physico-chemical and biological treatment. In most cases, even a combination of these purification methods cannot purify the water to the required level. Considering that water is the only consumable resource, it is important not only to purify it in accordance with the requirements, but also to update the purification methods for use in other necessary industries. The issue under consideration is aimed at wastewater treatment of the Aktau bitumen processing plant. The article presents the results of a study of the evaporation of wastewater from a bitumen plant in a solar installation without reagents. Laboratory experiments have shown the possibility of wastewater treatment by distillation at lower temperatures and pressures. Along with the wastewater treatment of a bitumen plant without reagents, it can also be considered as a source of the release of precious metals.

Defect Strategy in Solid-State Lithium Batteries.

Solid-state lithium batteries (SSLBs) have great development prospects in high-security new energy fields, but face major challenges such as poor charge transfer kinetics, high interface impedance, and unsatisfactory cycle stability. Defect engineering is an effective method to regulate the composition and structure of electrodes and electrolytes, which plays a crucial role in dominating physical and electrochemical performance. It is necessary to summarize the recent advances regarding defect engineering in SSLBs and analyze the mechanism, thus inspiring future work. This review systematically summarizes the role of defects in providing storage sites/active sites, promoting ion diffusion and charge transport of electrodes, and improving structural stability and ionic conductivity of solid-state electrolytes. The defects greatly affect the electronic structure, chemical bond strength and charge transport process of the electrodes and solid-state electrolytes to determine their electrochemical performance and stability. Then, this review presents common defect fabrication methods and the specific role mechanism of defects in electrodes and solid-state electrolytes. At last, challenges and perspectives of defect strategies in high-performance SSLBs are proposed to guide future research.

Novel Isomer of Volleyballene Sc20C60.

The Stone-Wales defect is a well-known and significant defective structure in carbon materials, impacting their mechanical, chemical, and electronic properties. Recently, a novel metal-carbon nanomaterial named Volleyballene was discovered, characterized by a C-C bond bridging two carbon pentagons. Using first-principles calculations, a stable Stone-Wales-defective counterpart of Volleyballene, exhibiting Th symmetry, has been proposed by rotating the C-C bond by 90°. Although its binding energy per atom is slightly higher than that of Volleyballene (ΔEb = 0.009 eV/atom), implying marginally lower structural stability, it can maintain its bond structure until the effective temperature reaches about 1500 K, indicating greater thermodynamic stability. Additionally, its highest vibration frequency is 1346.2 cm-1, indicating a strong chemical bond strength. A theoretical analysis of the Sc20C60 + Sc20C60 binary systems highlights that the stable building block may be applied in potential nanoassemblies.

Analysis of the initial reaction mechanism of TKX-50 based on Raman intensity.

Dihydroxylammonium 5,5'-biotetrazolium-1,1'-diolate (TKX-50) has two important properties of typical azole energy-containing ionic salts, including high energy and safety. Therefore, in today's era where more emphasis is placed on explosive performance and explosive detonation control conditions, TKX-50 is a very important object of research, and its reaction process in the initial stage of detonation is gradually receiving more and more attention from researchers in the field of energy-containing materials research. In this paper, based on first-principles density-functional theory (DFT), the mechanism of chemical bond breakage of TKX-50 under pressure was determined based on the analysis of the strength and stability of chemical bonds inside the TKX-50 molecules using Raman spectroscopy relative intensity analysis. The results show that TKX-50 is dominated by N-H bond breaking and followed by H-O bond breaking in the initial reaction stage. These reactions lead to the reorganization and structural changes within the molecule, which eventually lead to the decomposition of TKX-50.

Maldistribution of Chemical Bond Strength Inducing Exceptional Anisotropy of Thermal Conductivity in Non‐Layered Materials

AbstractCurrently, the efforts to find materials with high κ anisotropy ratios mainly focus on layered materials, however, the limited quantity and lower workability comparing to non‐layered ones boost the exploration of non‐layered materials with high κ anisotropy ratios. Here, taking PbSnS3, a typical non‐layered orthorhombic compound, as an example, we propose that maldistribution of chemical bond strength can lead to large anisotropy of κ in non‐layered materials. Our result reveals that the maldistribution of Pb−S bonds lead to obvious collective vibrations of dioctahedron chain units, resulting in an anisotropy ratio up to 7.1 at 200 K and 5.5 at 300 K, respectively, which is one of the highest ever reported in non‐layered materials and even surpasses many classical layered materials such as Bi2Te3 and SnSe. Our findings can not only broaden the horizon for exploring high anisotropic κ materials but also provide new opportunities for the application of thermal management.

Maldistribution of Chemical Bond Strength Inducing Exceptional Anisotropy of Thermal Conductivity in Non-Layered Materials.

Currently, the efforts to find materials with high κ anisotropy ratios mainly focus on layered materials, however, the limited quantity and lower workability comparing to non-layered ones boost the exploration of non-layered materials with high κ anisotropy ratios. Here, taking PbSnS3 , a typical non-layered orthorhombic compound, as an example, we propose that maldistribution of chemical bond strength can lead to large anisotropy of κ in non-layered materials. Our result reveals that the maldistribution of Pb-S bonds lead to obvious collective vibrations of dioctahedron chain units, resulting in an anisotropy ratio up to 7.1 at 200 K and 5.5 at 300 K, respectively, which is one of the highest ever reported in non-layered materials and even surpasses many classical layered materials such as Bi2 Te3 and SnSe. Our findings can not only broaden the horizon for exploring high anisotropic κ materials but also provide new opportunities for the application of thermal management.

Exploring Zn doped η′‐Cu6Sn5: Structural stability, fracture toughness and thermal conductivity

AbstractIn order to investigate the effect of alloying elements on mechanical properties of η′‐Sn‐Cu alloys, the effect of Zn‐doping on the structural stability, elasticity, electrical and thermodynamic properties of η′‐Cu6Sn5 intermetallic in Sn‐Cu alloys have been calculated by first‐principles calculations. The results show that the Zn‐doped η′‐Cu6Sn5 are thermodynamically and dynamically stable. The doped phase is the most stable when Zn replaces Cu1 site. The bulk modulus and shear modulus of η′‐Cu6Sn5 with Zn‐doped Sn1 site are the highest. When Zn replaces Sn, the stiffness is stronger than that when Zn replaces Cu, and the stiffness order is Zn–Sn > Zn–Cu > η′‐Cu6Sn5. Compared with other doping sites, the 3D surface configurations of elastic modulus of Zn–Sn1 η′‐Cu6Sn5 are the largest. In addition, Zn doping improves the fracture toughness and chemical bond strength of the material. The thermal conductivity and electron thermal conductivity of η′‐Cu6Sn5 also increased.

Hydrolysis and condensation of monobutyltin chloride: reaction process analysis with DFT.

As the initial process of preparing transparent conductive oxide materials from monobutyltin chloride (MBTC) to tin oxide, the hydrolysis and condensation of MBTC to form a dimer Sn2 play a critical role. However, the specific mechanism of this process is still unclear. Here we develop a step-by-step searching method based on density functional theory calculation and empirical chemical criteria to determine possible reaction pathways and reveal the most likely reaction mechanism. The wave function analyses of various intermediate species provide more insights into the changes of atomic charge population, chemical bond strength, and coordination situation of central tin in the reaction process. Further investigation on the ring-containing Sn2 reveals the existence of unique three-center four-electron (3c-4e) interactions to stabilize the four-membered Sn2O2 ring structure, which serves as the true driving force for dimerization reaction. These results provide a more detailed understanding of the hydrolysis and condensation process of MBTC and would be helpful for the future optimization of the preparation process of tin oxide films.

Thermodynamic explanation and criterion for the exhibition of melting inability in molecular species

<abstract> <p>Thermodynamic properties of matter e.g., melting point, are important for various applications. However, in some substances the primary observed effect upon heating is decomposition which in some cases is accompanied by fluidization. Thus, it would be very useful to be able to predict if a given substance will be able to melt or will exhibit melting inability upon heating. In this work, a thermodynamic explanation for the melting inability of molecular solids is provided and a corresponding criterion is proposed for the prediction of melting ability or inability of a given substance. One key concept is to study the strength of the weakest chemical bond rather than overall enthalpy of reaction. This arises from the fact that if decomposition occurs, then, regardless of the extent of decomposition, the transition cannot be considered to be melting. The criterion can be combined with sophisticated modeling in order to derive accurate values. Here, a simple method is proposed and an approximate index is developed which allows for a rapid and massive implementation of the criterion. The index is based on the concept of group contributions methods (estimation of the enthalpy of the maximum possible interactions, ${\mathit{\Delta}} H_{max }$) and on a distorted version of Trouton's rule (correlation of $ {\mathit{\Delta}} H_{max }$ with the heat required for melting). The correlation factor (${x}_{melting}$) was found to be equal to 40.6%. The index is successfully applied in various organic substances, including (bio)molecules of pharmaceutical/nutraceutical interest. Index values between −30 and 0 correspond to marginal cases of rather high uncertainty. Positive index values clearly point out melting inability. The proposed index successfully predicts the melting ability/inability in more than 80% of the studied substances.</p> </abstract>

Steering competitive N2 and CO adsorption toward efficient urea production with a confined dual site.

Electrocatalytic urea synthesis under mild conditions via the nitrogen (N2) and carbon monoxide (CO) coupling represents an ideal and green alternative to the energy-intensive traditional synthetic protocol. However, this process is challenging due to the more favorable CO adsorption than N2 at the catalytic site, making the formation of the key urea precursor (*NCON) extremely difficult. Herein, we theoretically construct a spatially isolated dual-site (DS) catalyst with the confinement effect to manipulate the competitive CO and N2 adsorption, which successfully guarantees the dominant horizontal N2 adsorption and subsequent efficient *NCON formation via C-N coupling and achieves efficient urea synthesis. Among all the computationally evaluated candidates, the catalyst with dual V sites anchored on 4N-doped graphene (DS-VN4) stands out and shows a moderate energy barrier for C-N coupling and a low theoretical limiting potential of -0.50 V for urea production, which simultaneously suppresses the ammonia production and hydrogen evolution. The confined dual-site introduced in this computational work has the potential to not only properly address part of the challenges toward efficient urea electrosynthesis from CO and N2 but also provide an elegant theoretical strategy for fine-tuning the strength of chemical bonds to achieve a rational catalyst design.

Effect of preheating on the physicochemical properties and bond strength of composite resins utilized as dental cements: An in vitro study

Statement of problemLittle is known regarding the use of preheated composite resins to bond indirect restorations and its impact on mechanical properties when compared with resin cements. PurposeThe purpose of this in vitro study was to compare the chemical and physical properties and bond strength to enamel and ceramics of preheated composite resins and resin cements. Material and methodsTwo composite resins, the microhybrid Filtek Z250XT and the nanoparticulate Z350XT were tested, and 2 commercially available resin cements, the dual-polymerized Rely-X ARC and the light-polymerized Rely-X Veneer were used as controls. A device (HotSet) was used to preheat the composite resins to 69 °C before light-polymerization. The following properties were tested: flexural strength, modulus of elasticity, fracture toughness, microshear bond strength to enamel and ceramics, degree of conversion, flow, sorption and solubility, and color stability. Statistical analysis was done with ANOVA and Holm-Sidak for multiple comparisons (α=.05). ResultsPreheating had no significant effect on the degree of conversion, flexural strength, fracture toughness, solubility, or microshear bond strength to the enamel of the tested composite resins (P>.05). However, preheating increased the sorption and reduced the microshear bond strength to the ceramic (P<.05). The flowability of the composite resins increased with heating but showed lower values when compared with both resin cements (P<.05). Color stability was more affected in the preheated composite resins than in the resin cements. ConclusionsThe preheating process resulted in little to no benefit in the evaluated properties for the composite resins. Resin cements appear to be the best option for cementing indirect restorations.

Effects of Vacancies on the Structural, Elastic, Electronic and Thermodynamic Properties of C11b-VSi2 by First-Principles Calculations

The effects of V and Si vacancies on structural stability, elastic properties, brittleness-toughness transition, Debye temperature and electronic properties of tetragonal C11b-VSi2 are investigated using the first-principles calculations. The vacancy formation energy and phonon dispersions confirm that perfect C11b-VSi2 and C11b-VSi2 with different atomic vacancies are thermodynamically and dynamically stable. The C11b-VSi2 with V-atom vacancies is more stable than that with Si-atom vacancies. The introduction of different atomic vacancies enhances the elastic modulus and its anisotropy of C11b-VSi2. The electron density difference and densities of state of perfect VSi2 and VSi2 with different vacancies are calculated, and the chemical bonding properties of perfect VSi2 and VSi2 with vacancies are discussed and analyzed. Additionally, the results show that the chemical bond strength of VSi2 is enhanced by the introduction of vacancies. Finally, Debye temperatures of perfect VSi2 and VSi2 with vacancies are also calculated.

Regulating the formation ability and mechanical properties of high-entropy transition metal carbides by carbon stoichiometry

• High-entropy transition metal carbides with regulatable carbon stoichiometry (HE TMC x ) achieve the promoting of formation ability from carbon stoichiometry deviations. • Bulk (Zr 0.25 Hf 0.25 Ta 0.25 Nb 0.25 )C x (SPS-ZHTNC x ) with carbon stoichiometry deviations show promoted sintering. • Bulk (Zr 0.25 Hf 0.25 Ta 0.25 Nb 0.25 )C x (SPS-ZHTNC x ) present tunable mechanical properties. Tremendous efforts have been dedicated to promote the formation ability of high-entropy transition metal carbides. However, the majority of methods for the synthesis of high-entropy transition metal carbides still face the challenges of high temperature, low efficiency, additional longtime post-treatment and uncontrollable properties. To cope with these challenges, high-entropy transition metal carbides with regulatable carbon stoichiometry (HE TMC x ) were designed and synthesized, achieving improved ability for single phase solid solutions formation, promoting of sintering and controllable mechanical properties. Two typical composition series, i.e., easily synthesized (Zr 0.25 Hf 0.25 Ta 0.25 Nb 0.25 )C (ZHTNC) and difficultly synthesized (Zr 0.25 Hf 0.25 Ta 0.25 Ti 0.25 )C (ZHTTC) are selected to demonstrate the promoting formation ability of single phase solid solutions from carbon stoichiometry deviations. Single phase high-entropy ZHTTC, which has been proven difficult in forming a single phase solid solution, can be prepared with the decrease of C/TM ratio under 2000 °C; while the high-entropy ZHTNC, which has been proven easy in forming a single phase solid solution, can be synthesized at lower temperatures with the decrease of C/TM ratio. The synergistic effect of entropy stabilization and reduced chemical bond strength gaining from carbon stoichiometry deviations is responsible for the formation of single phase solid solutions and the promoted sintering of HE TMC x . For example, the relative density of bulk (Zr 0.25 Hf 0.25 Ta 0.25 Nb 0.25 )C x (SPS-ZHTNC x ) increases from 90.98% to 94.25% with decreasing the C/TM atomic ratio from 0.9 to 0.74. More importantly, the room temperature flexural strength, fracture toughness and brittleness index of SPS-ZHTNC x can be tuned in the range of 384 MPa–419 MPa, 4.41 MPa⋅m 1/2 –4.73 MPa⋅m 1/2 and 3.679 μm −1/2 –4.083 μm −1/2 , respectively. Thus, the HE TMC x prepared by adjusting the ratio of carbon to refractory transition metal oxides have great potential for achieving low temperature synthesis, promoted sintering and tunable properties.

Liquid-Phase Exfoliation of Nonlayered Non-Van-Der-Waals Crystals into Nanoplatelets.

For nearly 15 years, researchers have been using liquid-phase exfoliation (LPE) to produce 2D nanosheets from layered crystals. This has yielded multiple 2D materials in a solution-processable form whose utility has been demonstrated in multiple applications. It wasbelieved that the exfoliation of such materials is enabled by the very large bonding anisotropy of layered materials where the strength of intralayer chemical bonds is very much larger than that of interlayer van der Waals bonds. However, over the last five years, a number of papers have raised questions about ourunderstanding of exfoliation by describing the LPE of nonlayered materials. These results are extremely surprising because, as no van der Waals gap is present to provide an easily cleaved direction, the exfoliation of such compounds requires the breaking of only chemical bonds. Here the progress in this unexpected new research area is examined. The structure and properties of nanoplatelets produced by LPE of nonlayered materials are reviewed. A number of unexplained trends are found, not least the preponderance of isotropic materials that have been exfoliated to give high-aspect-ratio nanoplatelets. Finally, the applications potential of this new class of 2D materials are considered.