Higher Bond Strength Research Articles

Crystallization, recrystallization and melting behaviors in supramolecular poly(l-lactic acid) bonded by metal-ligand coordination

The effect of metal-ligand coordination on crystallization and melting behaviors of polymers has not been comprehensively investigated. In this study, a series of supramolecular poly(l-lactic acid)s (SM-PLLAs) were prepared by changing various metal ions, length of polymer chains and stoichiometric ratio of ligands to metal ions (L/M). The complexation of metal ions with ligands in SM-PLLAs was confirmed by the intrinsic viscosity and UV–visible spectroscopy. It was found that crystallization rate and crystallinity of SM-PLLAs were strongly dependent on the chain length of precursor in both non-isothermal and isothermal crystallizations. With chain length of 1.6 kg/mol, crystallization of PLLA was completely suppressed regardless of the metal ions, whereas PLLA with longer chain length of 3.0 kg/mol exhibited strong dependence of the type of metal. During the heating process, melting behaviors can be tuned by the strength of metal-ligand coordination, temperature and the degree of complexation. Unlike PLLA precursor and SM-PLLA coordinated with Cu2+ exhibited multiple melting behaviors, only a single melting peak was appeared in PLLA bonded with Co2+, indicative of suppression of recrystallization during heating. With ratio of ligand to Co2+ increased from 1:1 to 6:1, crystallization and melting behaviors were tuned by the content of free and bounded PLLA chains. As compared to Cu2+, SM-PLLA coordinated with Co2+ exhibited higher complex modulus and viscosity due to the high bond strength, as well as a more stable structure underwent heating and shear, making diffusion of polymer chains and the structural adjustment more difficult. This work may shed light on understanding the intricate interplay of metal-ligand coordination effects on the crystallization and melting behaviors of polymers, which may be helpful with the design and making out the relationship between structure and properties of supramolecular polymers.

Laser Engineering Nanocarbon Phases within Diamond for Science and Electronics.

Diamond, as the densest allotrope of carbon, displays a range of exemplary material properties that are attractive from a device perspective. Despite diamond displaying high carbon-carbon bond strength, ultrashort (femtosecond) pulse laser radiation can provide sufficient energy for highly localized internal breakdown of the diamond lattice. The less-dense carbon structures generated on lattice breakdown are subject to significant pressure from the surrounding diamond matrix, leading to highly unusual formation conditions. By tailoring the laser dose delivered to the diamond, it is shown that it is possible to create continuously modified internal tracks with varying electrical conduction properties. In addition to the widely reported conducting tracks, conditions leading to semiconducting and insulating written tracks have been identified. High-resolution transmission electron microscopy (HRTEM) is used to visualize the structural transformations taking place and provide insight into the different conduction regimes. The HRTEM reveals a highly diverse range of nanocarbon structures are generated by the laser irradiation, including many signatures for different so-called diaphite complexes, which have been seen in meteorite samples and seem to mediate the laser-induced breakdown of the diamond. This work offers insight into possible formation methods for the diamond and related nanocarbon phases found in meteorites.

Room temperature wafer bonding through conversion of polysilazane into SiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {SiO}_{2}$$\\end{document}

Room temperature wafer bonding is a desirable approach for the packaging and assembly of diverse electronic devices. The formation of SiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {SiO}_{2}$$\\end{document} layer at the bonding interface is crucial for a reliable wafer bonding as represented by conventional bonding techniques such as hydrophilic bonding and glass frit bonding. This paper reports a novel concept of room temperature wafer bonding based on the conversion of polysilazane to SiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {SiO}_{2}$$\\end{document} at the bonding interface. As polysilazane is converted to SiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {SiO}_{2}$$\\end{document} by hydrolysis, in this work, adsorbed water is introduced to the bonding interface by plasma treatment, thereby facilitating the formation of SiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {SiO}_{2}$$\\end{document} at the wafer bonding interface. The experimental results indicate that the adsorbed water from the plasma treatment diffuses into the polysilazane layer and facilitates its hydrolysis and conversion. The proposed method demonstrates the successful wafer bonding at room temperature with high bond strength without interfacial voids. This technique will provide a new approach of bonding wafers at room temperature for electronics packaging.

Preparation and properties of gradient fire & corrosion protection magnesium phosphate cement coatings

Fire and corrosion protection are the main problems limiting the application of steel. Gradient fire & corrosion protection coating for steel structures was prepared by magnesium phosphate cement (MPC) with high bond strength, excellent anti-corrosion, and high-temperature resistance. The interface inside the MPC coating and of the MPC coating and steel plate were observed. The bonding strength, corrosion, and fire performance of MPC coating were investigated before and after dry-wet cycles. The results showed MPC had high bond strength with itself even under dry-wet cycle conditions. Only 6 mm MPC coating can meet the fire and corrosion resistance of steel structures. When the total thickness of MPC coating was 6 mm, the rising thickness (0–1.6 mm) of MPC paste improved the bond strength to 2.5 times and anticorrosive performance but reduced the fireproof performance of MPC coating. Even though the thickness of the MPC paste was 1.6 mm, the fireproof performance of MPC coating remained abundant. After 28 dry-wet cycles, the fireproof performance of MPC coating with 0.4 mm MPC paste was comparable to that before the dry-wet cycle. The bond strength was still more than 0.3 MPa, which can still meet the requirements of the specification.

Seismic behavior of a new type of precast concrete shear wall using UHPC connections at boundary elements

Ultra-high Performance Concrete (UHPC) is an attractive choice for connecting Precast Concrete Shear Walls (PCSWs), because of its high bond strength with rebars allowing for reduced lapped rebar lengths and precision requirements. This paper proposes a new type of PCSW that uses UHPC connections only at the boundary elements, significantly streamlining the installation process of wall panels and improving construction efficiency. To evaluate its seismic behavior, a total of five walls comprising three PCSWs and two Cast-In-Place (CIP) walls were tested by cyclic loadings under both low and high axial loads. Similar failure modes characterized by bending-shear damage were captured in all five specimens. The proposed precast walls display 7.8%–8.1% greater bearing ability and 41.8% higher ductility in comparison to CIP counterparts. These precast walls also demonstrated superior energy dissipation ability, particularly under high axial loads. Following NEHRP, it was validated that the proposed precast walls using UHPC connections at boundary elements could be used in regions with high seismic activity. Moreover, the finite element (FE) models were developed, yielding simulated results that aligned reasonably with the experimental findings, and the parametric predictions were performed to further broaden the scope of experimental works.

Filling Material Bond Strength to Dentin Is Positively Influenced by the Agitation of Endodontic Final Irrigating Solutions.

The final step of irrigation has been considered to of increase the bonding strength of filling material to dentin. This study investigated the impact of three final-step irrigation methods on the endodontic sealer bond strength to dentin by using a micro push-out test. Palatal roots of human maxillary molars were cleaned and shaped and randomly divided in six groups (n=15) according to the final-step irrigation method and the type of root canal sealer used. The solutions used for the final-step irrigation were 17% ethylenediaminetetraacetic acid and 2.5% sodium hypochlorite, which underwent three methods: 1) syringe-needle irrigation/conventional, 2) passive ultrasonic irrigation, and 3) XP-endo Finisher agitation. The root canal sealers used were: EndoSequence BC Sealer, and AH-Plus sealer. Roots were obturated with the single cone technique and then, cross-sectioned in 2-mm-thick slices (3 slices from each root). Push-out test was performed on the sliced specimens (cervical, middle, and apical thirds) with a universal testing machine. Bond strength values were recorded in megapascal (MPa). Subsequently, each specimen was longitudinally split to verify the type of failure. Data analysis was performed using Johnson transformation, three-way analysis of variance, Tukey's post-hoc tests, and the partial Eta squared test. There were significant differences in bond strength between the sealers [AH: 4.46±2.24 and BC: 3.47±2.19 MPa (P<0.001)]; between final-step irrigation methods [passive ultrasonic irrigation: 4.52±2.25, XP-endo Finisher: 3.93±3.93 and syringe-needle irrigation/conventional: 3.37±2.51 MPa (P<0.001)], and between the root canal thirds represented by the sliced specimens [cervical: 5.45±2.39, middle: 4.14±1.99 and apical: 2.30±1.30 MPa (P<0.001)]. The interaction between the variables had no significance (P>0.05). Agitation of the final irrigating solution may improve the bonding of the sealer to canal walls. AH-Plus sealer had the highest bond strength. The bond strength reduced significantly towards the apical third.

Enhancing bond performance: Carbon fiber reinforced polymer bar interaction with multi-walled carbon nanotubes cementitious composites in chloride-exposed conditions

A number of studies have been conducted on strengthening structures using carbon fiber reinforced polymers (CFRP) and improving the performance of cement fillers using multi-walled carbon nanotubes (MWCNT). In this study, bond characteristics of CFRP bars to MWCNT cementitious composites is investigated in chloride environment. The bonding advantage of CFRP bars and MWCNT cement filler is due to the mechanical properties of MWCNT and the ability to utilize the corrosion resistance provided by CFRP. This enables highly durable composites that can resist corrosion in chloride-rich environments. A total of 36 pullout (PO) tests were performed on CFRP bars set into MWCNT cementitious composites. Mercury Intrusion Porosimetry (MIP) test and field-emission scanning electron microscopy (FE-SEM) confirmed a decrease in porosity upon addition of MWCNTs. MWCNTs filled the pores of cement with nanoscale particles and increased the bond area of the cement composite with CFRP bar. The reduction in porosity between cement and aggregate not only enhanced strength but also improved chloride resistance. However, agglomeration began at 1.0-wt% concentration owing to van der Waals forces. The results revealed that the 0.5-wt% MWCNT cementitious composite with CFRP bars had the highest bond strength in a chloride environment.

The effect of immediate dentin sealing on the bond strength of resin composite to dentin bonded with universal bonding agent: An in vitrostudy

Background:Dentin hypersensitivity is a common scenario encountered in dental practice. This issue can be treated by reducing dentin permeability and dentinal fluid flow. However, the desensitizing agents used may adversely affect the bonding of composite restorations to dentin.Aim:To evaluate the shear bond strength of restorative composites to dentin treated with silver diamine fluoride and self-etch bonding agent bonded using a universal bonding agent.Materials and methods:A total of 30 teeth were selected, and their occlusal surfaces were ground to expose a flat dentin surface. The teeth were then embedded in cold cure resin blocks. Depending on the treatment, the samples were randomly divided into three groups, with 10 in each. The samples in the group were untreated, in group 2 were treated with Silver Diamine Fluoride (SDF), and in group 3 with the sixth generation bonding agent (self-etch primer). After the treatment, the composite is bonded to the dentin surfaces and subjected to shear bond strength using the universal testing machine (UTM). The specimen was mounted on the custom-made jig and placed over the UTM. The load was applied at a cross-head speed of 1mm/min until debonding occurred at the dentin and composite interface, and the bond strength was computed in MPa. Overall comparisons were analyzed using the Kruskal-Wallis test. The Mann-Whitney U-test was used for pair-wise comparisons, and the significance level was set at p &lt; 0.05.Results:The lowest bond strength was observed with the dentin surfaces treated with silver diamine fluoride (Group 2), and the highest bond strength was for dentin treated with self-etchbonding agent (Group3). Significant differences (p=0.003) were observed between the groups. In pair-wise comparisons, group 3 showed significant difference with group 1 (p=0.007) and group 2 (p=0.002). However, no significant difference was observed between groups 1 and 2 (p=0.197).Conclusion:The shear bond strength varies with different desensitizing treatments. This study reported more SBS with sixth-generation bonding agent followed by untreated dentin and SDF.

Strengthening of bridges with iron-based shape memory alloy bars embedded in UHPFRC

Bridges are designed for a service life of up to 100 years. A significant number of structures still in use lack the required levels of structural safety, either due to deterioration or because older design codes are partly obsolete. With the increasing focus of the construction industry towards sustainability and circularity, there is a trend to develop innovative and efficient strengthening methods that enable the rehabilitation of under-designed or damaged structural components rather than rebuilding new structures. To this end, this paper presents a research project aiming at developing a new method for flexural strengthening of bridge decks, which consists in applying a layer of Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) reinforced with Iron-based Shape Memory Alloy (Fe-SMA) ribbed bars on top of the existing Reinforced Concrete (RC) structure. The Fe-SMA bars are activated through heating, ultimately leading to the development of prestressing forces.To analyse this novel technology, a case study is developed. The performance of the new system is compared to a strengthening using B500B steel reinforcing bars embedded in UHPFRC, highlighting the main advantages of the new method. Furthermore, the bond behaviour of Fe-SMA bars embedded in UHPFRC is characterised in detail through short pull-out tests. Design parameters such as the temperature of activation of Fe-SMA and concrete cover thickness are studied. The bond shear stress-slip relationships show very high bond strengths for all tested covers, even after a slight deterioration of the bond properties resulting from the heating.

Oxide-Free SiC-SiC Direct Wafer Bonding and Its Characterization

There are different requirements for the production process and the final product of SiC-SiC wafer bonding. The manufacturing of devices that are sensitive to high temperature processing – due to broadened doping profiles and induced thermal stresses – requires room temperature bonding with high bond strength, while for electrical devices, it is mandatory that the bonding interface with a thin amorphous layer is oxide-free.[1] Reduced complexity of processes is also an important point for the final production. Hence, the goal of this work was to perform and characterize direct bonding of SiC-SiC without any added/deposited bonding layer. This type of bonded SiC wafers can be used for power electronics such as for the fabrication of traction inverter for automotive applications, DC/DC converter, on board charger or charging station.[2]For the wafer bonding processes standard 100 mm 4H SiC wafers were bonded with their Si-terminated faces in order to fabricate oxide-free bonds. The wafer bonding process was performed using the EVG ComBond® system: first the native oxides from both wafer surfaces were removed using an ion beam sputtering process, followed by the transfer of both wafers to the bonding process station operated in ultra-high vacuum (UHV) to significantly retard the oxidation process. Finally, the bonding process was performed at room temperature (RT).The goal of this study was to demonstrate the feasibility of the bonding process and to gain insight on the surface chemistry after activation. The investigations covered three areas: incoming inspection of the original wafer, characterization of activated single wafer and analysis of bonded wafer pairs. The focus was on compositional, chemical, mechanical and morphological analysis of the surfaces and of the bonded interfaces. In the case of single wafers, the focus of the incoming inspection was on whether the wafers fulfill the requirements of wafer bonding, and on the characterization of activated wafers to measure the surface modifications. Atomic force microscopy (AFM), white light interferometry (WLI) and spectroscopic ellipsometry (SE) were used to determine the surface roughness, the wafer topography and the surface layer structure, respectively. All three parameters are essential for successful RT SiC-SiC wafer bonding. The change of the surface chemistry was investigated by angle resolved x-ray photoelectron spectroscopy (AR-XPS). The quality of the bonded wafers and the bonding energy were verified using scanning acoustic microscopy (SAM) measurements (Fig. 1) as well as the Maszara blade test. Furthermore, cross-section transmission electron microscopy (X-TEM) showed a bonding interface with a thin amorphous layer and no noticeable additional oxygen containing layer (Fig. 2). In order to gain quantitative elemental distributions of oxygen and argon, energy dispersive x-ray spectroscopy (EDXS) was applied.The work reported is a demonstration of the capability of the different characterization methods regarding SiC-SiC wafer bonding. Future work will focus on the investigation of the bonded interface characteristics in the function of the bonding process parameters and the annealing conditions.[1] F. Mu, M. Fujino, T. Suga, Y. Takahashi, H. Nakazawa and K. Iguchi, "Wafer bonding of SiC-SiC and SiC-Si by modified surface activated bonding method" 2015 International Conference on Electronics Packaging and iMAPS All Asia Conference (ICEP-IAAC), Kyoto, Japan, 2015, pp. 542-545, doi: 10.1109/ICEP-IAAC.2015.7111073.[2] Tsunenobu Kimoto, "Material science and device physics in SiC technology for high-voltage power devices" Jpn. J. Appl. Phys. 54 040103 (2015), doi: 10.7567/JJAP.54.040103. Figure 1

Effect of ethanolic extract of propolis on antibacterial and microshear bond strength of glass-ionomer restorations to dentin

ObjectivesThis study was conducted to evaluate the effect of ethanolic extract of propolis on antibacterial and microshear bond strength of glass ionomer restorations to dentin. Materials and methodsConventional glass ionomer cement (Equia forte, GC Tokyo, Japan), resin-modified glass ionomer (Fuji II LC, GC Tokyo, Japan) and propolis powder (dried extract from honey bees) materials were used in this study. Both conventional glass ionomer and resin-modified glass ionomer were modified by two different concentrations of ethanolic extract of propolis (10 % and 25 % EEP). For antibacterial test, Streptococcus mutans strain was spread on agar petri dishes using a sterile swab. Discs of both glass ionomer restorative materials (without adding EEP, with 10 % EEP and with 25 % EEP) were fabricated within the agar plates. Antibacterial activity was evaluated by measuring the inhibition zones around each disc. For microshear bond strength test, 60 healthy human permanent molars were prepared by cutting occlusal surface and expose the dentin at the height of contour of all teeth then conditioned using poly acrylic acid conditioner, both glass ionomer restorative materials (without adding EEP, with 10 % EEP and with 25 % EEP) were mixed and applied on conditioned dentin surface by using tygon tube. Microshear bond strength was evaluated by the universal testing machine. ResultsTwo-way ANOVA test revealed that both glass ionomer type and different concentrations of EEP had significant effect on the antibacterial test results and microshear bond strength values (p < 0,05). Glass ionomer restorative material with 25%EEP had the highest antibacterial values whereas glass ionomer restorative material without modifications (control groups) had the lowest values. Resin-modified glass ionomer without any modification (control group) had the highest bond strength while resin-modified glass ionomer with 25%EEP had the lowest bond strength. ConclusionsIncorporation of ethanolic extract of propolis to glass ionomer restorative material increases the antibacterial effects of both conventional GIC and RMGI. Inspite of this advantage, it seems that it has deleterious effect on microshear bond strength to dentin.

Reliability evaluation of thick Ag wire bonding on Ni pad for power devices

In recent years, silicon carbide (SiC) semiconductors have gained traction in high-performance power devices due to their ability to operate at high temperatures (above 200 °C). However, traditional interconnection materials are not sufficiently reliable at such elevated temperatures. Typically, in power devices, thick Al wires with diameters of 200 μm or larger are commonly used to bond Al electrodes of semiconductor chips to their corresponding Cu leadframes or substrates. Nevertheless, the low melting point of Al can lead to recrystallization at high temperatures, thereby raising concerns about reliability and a decrease in wire strength and fatigue properties. Although thick Cu wires with higher melting points have been explored as potential solutions, their high hardness and susceptibility to work hardening during bonding can damage the chip beneath the bonding area, making them impractical. In response to these challenges, we investigated the use of thick Ag wires. However, direct bonding of thick Ag wires to Al pads can form intermetallic compounds (IMC) in the bonding area, leading to concerns about decreased reliability. To address this issue, we experimented with a bonding method that utilized thick Ag wires on Ni pads. In this study, we evaluated the reliability of thick Ag wire bonding under various stress conditions, including high-temperature storage tests (HTST) and temperature cycling tests (TCT). Our results showed that thick Ag wire bonding on Ni pads exhibited high bond strength and prevented IMC formation after HTST. Nonetheless, bond failure of the Ag wires could occur after TCT due to the mismatch in the coefficient of thermal expansion (CTE) between the Ag wire and SiC chip, particularly under extremely severe TCT conditions. We found this issue could be mitigated by introducing a soft metal layer, such as Al, between the Ni pad and the SiC chip. This reduced internal stress and enabled the device to pass TCT under harsher conditions with reliable performance.

Pull‐off capacity of FRP–concrete composite bonded with epoxy/geopolymer at elevated temperature

AbstractExternally bonded strengthening technique to the concrete has been widely used with epoxy adhesive. However, the adhesive is considerably weak against high temperatures, which has been regarded as the critical point in the loss of integrity of the strengthened system. Alternatively, geopolymer materials have shown an excellent performance at high temperatures, thus, their potential to be used as adhesive material has been investigated in this work. In experimentation, the composite specimens were developed using both types of adhesives, epoxy and geopolymer, and their performance was evaluated at three temperature levels (20, 60, and 120°C) by conducting pull‐off strength tests and classifying their failure modes. It was observed that the strength of concrete and epoxy was reduced with temperature. In contrast, the strength of geopolymer‐based adhesives strength was increased due to the reactivity of the precursor at high temperatures. Also, bond strength was reduced for both composite specimens at elevated temperatures. The highest bond strength was observed for the epoxy‐based adhesive system at 20°C, and about 70% loss in bond strength was observed when exposed to 120°C. The failure mode was also shifted from concrete to adhesive interface failure, that is, failure between the adhesive and the fiber fabric layer. The geopolymer‐based adhesive system has lower strength than its counterpart at all temperature levels, and the failure mode was adhesive interface failure. To enhance the bonding capacity at high temperatures, efforts are being made by adding different minerals has been employed. From the experimental results, it was found that there were some improvements, however, it was still less than that of epoxy‐based system. Further optimization of the geopolymer adhesive using minerals is required and then high‐thermal resistance geopolymer adhesive can be established.

Evaluation of the marginal adaptation and debonding strength of two types of CAD-CAM implant-supported cement-retained crowns

BackgroundIn-vitro data from a clinically well-known lithium disilicate ceramic reference was used to assess the expected performance of resin-based materials in implant dentistry. The purpose of the study was to compare the bond strength and marginal adaptation of nano-ceramic hybrid composite crowns cemented to stock cement-retained abutments to lithium disilicate crowns.MethodsTwenty abutment analogs were embedded into auto-polymerizing acrylic resin blocks. The blocks were divided into 2 groups according to the restorative crown material. The 2 groups were divided as follows: Resin nano-ceramic group and lithium disilicate group. Abutment analogs in both groups were scanned using a laboratory scanner, and the restorations were designed, manufactured, and cemented with resin cement over the corresponding group. All samples were tested for marginal adaptation and bond strength after storage for 24 hours at 37 °C in 100% humidity. Data were collected, tabulated, and statistically analysed using the appropriate tests. Normality was checked using Shapiro Wilk test and Q-Q plots. Data were normally distributed. Variables were presented using mean, 95% Confidence Interval (CI) and standard deviation in addition to median and Inter Quartile Range (IQR). Differences between groups regarding debonding forces was assessed using independent t test. Two Way ANOVA was performed to assess the effect of material and bonding on marginal gap. All tests were two tailed and p value was set at < 0.05.ResultsMarginal gap and debonding force values were significantly different according to the type of material used (P < .05). Resin nano-ceramic crowns presented lower marginal gap values before (20.80 ± 8.87 μm) and after (52.11 ± 22.92 μm) bonding than lithium disilicate crowns. The debonding force value for resin nano-ceramic crowns (284.30 ± 26.44 N) was significantly higher than that for lithium disilicate crowns (253.30 ± 33.26 N). Adhesive failure mode was detected in all the specimens in both groups.ConclusionsThe type of material used for implant-supported cement-retained crowns had a statistically significant effect on marginal adaptation and bond strength. Resin nano-ceramic implant-supported cement-retained crowns had better marginal adaptation and higher bond strength than those manufactured using lithium disilicate.

Alkali-Activated Slag Coatings for Fire Protection of OPC Concrete

During a fire, ordinary Portland cement (OPC) systems lose their mechanical properties. For this reason, it is important to find a way to protect it. This study suggested alternative uses of slag and phosphogypsum to produce coatings for fire-resistant applications. Five compositions of 10 mm thick alkali-activated slag coatings were investigated. In these compositions, different amounts of phosphogypsum (1%, 3%, 5%, 7%, and 10%) were used. In the first stage of this study, the residual compressive strength of samples with the coatings based on alkali-activated slag was compared to the results of OPC concrete samples without coatings. The experimental results showed that a higher residual compressive strength of 33.2–47.3 MPa OPC concrete was achieved for the samples with coatings. Meanwhile, the residual compressive strength of the uncoated samples was 32.37 MPa. In the second stage, OPC concrete samples were reinforced with fiberglass polymer (FRP) rods, and they had a similar positive effect on alkali-activated coatings. After exposure to higher temperatures, the pullout tests of the glass FRP bars showed that the adhesion strength was (9.44 MPa) 43.9% higher for the samples with coatings compared to the samples without coatings (6.56 MPa). Therefore, a higher bond strength can be maintained between concrete and FRP bars. Alkali-activated slag with 3% phosphogypsum can be used for the production of fire-resistant coating. These coatings could protect OPC concrete and reinforced concrete with glass FRP bars from fire.

Study of Conditional Glass Formers (II) on Basics of Optical Electronegativity

Concept of Electronegativity is used by so many researchers to calculate Refractive index Band energy, Dielectric constant, Metallization criterion, Basicity, Oxide ion polarizability, Bond ionicity, Third order non-linear optical susceptibility to study the so many glass systems. Here the concept of optical electronegativity is used to study these parameters for conditional glass formers refer as (II) of group V(A,B) and VI(A,B). They are Ta2O5, Nb2O5, V2O5, Cr2O3, Bi2O3, TeO2, MoO3, As2O3, WO3, Se2O3. It is observed that on decreasing the values of optical electronegativity, optical band energy, metallization criterion, and bond iconicity decreases; and optical dielectric constant, optical basicity, oxide ion polarizability refractive index, third order non linear optical susceptibility increases. All conditional glass forming oxides (II) are according to Pauling's packing rule, Goldschmidt radius ratio rule, Zachariasen's random network theory and rules for formation of glass and Sun’s single bond strength theory. For Conditional glass formers (II) radius ratio rc/ra = 0.250-0.492, [except Bi2O3 (0.75) &amp; TeO2 (0.87)] and single bond strength greater than 90 Kcal/mol. According to Sun’s, high bond strength oxides are not good glass formers because they themselves do not forms glass; but when they forms small ring in the melt of these materials which would result in easy crystallization. Key Words: Refractive index Band energy, Dielectric constant, Metallization criterion, Basicity, Oxide ion polarizability, Bond ionicity, Third order non-liner optical susceptibility.

Structuring step dependent characteristics in joining using pin-like structures in the vibration welding process

Abstract With this study, correlations in the structuring step of pin-like joining were derived. Increased friction energy due to higher amplitude or force leads to a reduction in structuring time. Changes in thermo-mechanical properties for humid specimens result in increased process times. The theoretical geometry of the pin-like structures is well reproduced in the lower pin area, regardless of the process control. In the upper pin area, increased force and amplitude results in increased defects and air inclusions as a result of an accelerate and more inhomogeneous pin formation. Humidity does not affect the general pin geometry, but should be avoided due to increased air inclusions that can weaken the structure. For the multi-material joints, high bond strengths of up to 30 % of the base material (max. 50 % possible with the geometry used) can be achieved. Therefore, a minimum undercut is required. Once this is reached, the pin defects and the corresponding pin-foot ratio are decisive for the resulting bond quality.

High-performance timber-concrete-composites with polymer concrete and beech wood

The performance of adhesive-bonded timber-concrete-composites (TCC) can be enhanced by using beech wood and polymer concrete (PC). In this work, two different PCs with an epoxy- and a polyurethane (PUR)-based matrix were investigated for application in TCCs. The mechanical performances were tested in dry and wet state by small-scale shear tests and flexural tests. Epoxy-PC showed high bond strength to beech with a shear strength of 16.7 ± 3.0 MPa compared to 3.2 ± 1.7 MPa observed with PUR-PC. Characterization of the swelling strain with digital image correlation (DIC) showed superior water stability of the epoxy-PC compared to PUR-PC. The results indicate that PCs, especially epoxy-PC, could be viable replacements for cement-based concrete in TCCs.

Effects of ion occupancy and polarizability on the crystal structure and microwave dielectric properties of CaEuCO4 (C[dbnd]Ga, Al) ceramics

CaEuCO4 (CGa, Al) microwave dielectric ceramics were produced through a solid-state reaction. Orthorhombic olivine CaEuGaO4 (pnma) exhibits a lower permittivity (εr = 9.7), a higher quality factor (Q × f = 82,049 GHz), and a larger negative resonant frequency temperature coefficient (τf = −54.6 ppm/°C). CaEuAlO4, which has a similar chemical formula, exhibits a perovskite-like structure (I4/mmm, K2NiF4-type), and its microwave dielectric properties are εr = 18.9, Q × f = 43,132 GHz, and τf = −1.6 ppm/°C. The difference in their structures is mainly caused by the properties of the Ga (III) atom. The difference in their dielectric properties can be proved to be affected by the “rattling” effect of Eu3+ through the bond valence theory. The relationship between the covalence (fc) and the bond strength (S) was investigated, and the higher bond strength might be the main reason for the higher Q × f in CaEuGaO4 ceramic.

Study of Conditional Glass Formers (I) on Basics of Optical Electronegativity

Concept of Electronegativity is used by so many researchers to calculate Refractive index, Band energy, Dielectric constant, Metallization criterion, Basicity, Oxide ion polarizability, Bond ionicity, Third order non-linear optical susceptibility to study the so many glass systems. Here the concept of optical electronegativity is used to study these parameters for conditional glass formers referred as (1) taken from group III (A,B) and IV (A,B); they are Y2O3, HfO2, ZrO2, Sc2O3, TiO2, Al2O3, In2O3, Ga2O3, and SnO2. It is observed that optical band energy, metallization criterion, and bond iconicity decreases; and optical dielectric constant, optical basicity, oxide ion polarizability refractive index and third order non linear optical susceptibility increases. All conditional glass formers (I) oxides are according to Pauling's packing rule, Goldschmidt radius ratio rule, Zachariasen's random network theory, rules for formation of glass and Sun’s single bond strength theory. For conditional glass formers (I) radius ratio rc/ra = 0.40-0.75 and single bond strength greater than 90 Kcal/mol. According to Sun’s, high bond strength oxides are not good glass formers because they themselves do not forms glass; but when they forms small ring in the melt of these materials which result in easy crystallization. Key Words: Refractive index Band energy, Dielectric constant, Metallization criterion, Basicity, Oxide ion polarizability, Bond ionicity, Third order non-liner optical susceptibility.