Shear bond strengths of two newly marketed self-adhesive resin cements to different substrates: A light and scanning electron microscopy evaluation

The purpose of this in vitro study was to compare the shear bond strengths (SBSs) of two newly marketed self-adhesive resin cements (RCs) to enamel, dentin, and lithium disilicate (LiSi) glass ceramic block. Forty-eight enamel and 48 dentin substrates were obtained from sound human molars. Additionally, 6 × 7 × 5 -mm- sized 24 specimens were produced from LiSi glass ceramic blocks. The tooth specimens were randomly assigned into four groups (n = 12) according to the surface treatments: (1) G-CEM ONE (GCO), (2) G-CEM ONE Adhesive Enhancing Primer (GCO-AEP) + GCO, (3) RelyX Universal (RXU), and (4) Scotchbond Universal Plus (SUP) + RXU. LiSi specimens were randomly divided into two groups (n = 12): (1) G-MultiPrimer (GMP) + GCO and (2) SUP + RXU. Following the RC applications, all specimens were kept in 100% humidity at 37°C for 24 hr and then submitted for SBS testing in a universal testing machine (1 mm/min). Data were analyzed by Welch's, one-way analysis of variance and two independent samples t tests. The nature of failures was examined under a light microscope, and scanning electron microscopy analyses were also performed for interfaces. GCO and RXU showed similar SBS to enamel (p > .05), and the use of adhesives resulted in improved SBS (p < .05). No difference was detected between GCO-AEP + GCO and SUP + RXU. The GCO-AEP + GCO exhibited the highest SBS to dentin (p < .05), followed by GCO ≥ SUP + RXU > RXU (p < .05). There was no significant difference between SBSs of two RCs to LiSi blocks (p > .05). No cohesive failure was determined for the tested groups by light microscope. The use of adhesives prior to the application of self-adhesive RCs improved their bonding to tooth tissues. GCO demonstrated superior SBS to dentin, whereas both self-adhesive RCs generated similar SBS to enamel and LiSi glass ceramic surfaces.     

Antibacterial and Cellular Behaviors of Novel Zinc-Doped Hydroxyapatite/Graphene Nanocomposite for Bone Tissue Engineering

Bacteria are one of the significant causes of infection in the body after scaffold implantation. Effective use of nanotechnology to overcome this problem is an exciting and practical solution. Nanoparticles can cause bacterial degradation by the electrostatic interaction with receptors and cell walls. Simultaneously, the incorporation of antibacterial materials such as zinc and graphene in nanoparticles can further enhance bacterial degradation. In the present study, zinc-doped hydroxyapatite/graphene was synthesized and characterized as a nanocomposite material possessing both antibacterial and bioactive properties for bone tissue engineering. After synthesizing the zinc-doped hydroxyapatite nanoparticles using a mechanochemical process, they were composited with reduced graphene oxide. The nanoparticles and nanocomposite samples were extensively investigated by transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. Their antibacterial behaviors against Escherichia coli and Staphylococcus aureus were studied. The antibacterial properties of hydroxyapatite nanoparticles were found to be improved more than 2.7 and 3.4 times after zinc doping and further compositing with graphene, respectively. In vitro cell assessment was investigated by a cell viability test and alkaline phosphatase activity using mesenchymal stem cells, and the results showed that hydroxyapatite nanoparticles in the culture medium, in addition to non-toxicity, led to enhanced proliferation of bone marrow stem cells. Furthermore, zinc doping in combination with graphene significantly increased alkaline phosphatase activity and proliferation of mesenchymal stem cells. The antibacterial activity along with cell biocompatibility/bioactivity of zinc-doped hydroxyapatite/graphene nanocomposite are the highly desirable and suitable biological properties for bone tissue engineering successfully achieved in this work.     

β-SiC production by reacting silica gel with hydrocarbon gas

A novel synthesis process, developed for producing high purity, submicron, non-agglomerated and low cost -SiC powders. The process is based on carbothermal reduction reaction of a novel coated precursor. The precursor is derived from a silica gel and a hydrocarbon gas and provides high contact area between reactants. This yields a better distribution of carbon within the silica gel and results in a more complete reaction and a purer product. The powders produced in this process have a low oxygen content (less than 0.8 wt.%), very fine particle size (0.1–0.3 m), narrow particle size distribution, non-agglomerated and are low cost. The sintering tests demonstrated that these powders can be pressureless-sintered to near theoretical density at about 2100°C in an inert atmosphere. No decarburization and no acid purification process was required before sintering.     

A 1.6-mm,metal tube ultrasonic motor

A miniaturized metal tube ultrasonic motor, the dimensions of which are 1.6 mm in diameter and 6 mm in length, was developed. Two flattened surfaces with 90 degrees were ground on the outer surface of the stator. Two PZT-based piezoelectric ceramics were bonded onto these flat surfaces. The asymmetrical surface of the stator developed the split of the two degenerated orthogonal bending modes, resulting in a wobble motion. The working frequency of the 1.6-mm motor with 6 mm in length was 130 kHz. A torque of 0.5 mNm was reached at a maximum power of 45 mW with a speed of 45 rad/sec. The maximum efficiency was 16%.     

Complex assembly variant design in agile manufacturing. Part II: Assembly variant design methodology

In the first paper of this two-part series, the assembly variant design system architecture and complementary assembly methodology were presented. The general complementary assembly models, hierarchical assembly model and relational assembly model, are established which were further specified as the Assembly Variants Model (AVM) and the Assembly Mating Graphs (AMGs) respectively to cater for the needs for assembly variant design. This paper discusses the assembly variant design methodology which is based on these assembly models. The matching components are searched and retrieved from the AVM and then the constraint groups are identified by manipulating the AMGs. Then the assembly variant design process is formulated as a mixed-integer (linear or non-linear) programming problem which is solved using a standard solver or heuristic. This methodology provides a systematic approach to facilitate the variant design of complex assembly products in the agile manufacturing environment. Finally, a prototype system is developed and examples are presented.     

Piezoelectric micromotor using a metal-ceramic composite structure

This paper presents a new piezoelectric micromotor design, in which a uniformly electroded piezoelectric ring bonded to a metal ring is used as the stator. Four inward arms at the inner circumference of the metal ring transfer radial displacements into tangential displacements. The rotor ends in a truncated cone shape and touches the tips of the arms. A rotation takes place by exciting coupled modes of the stator element, such as a radial mode and a second bending mode of the arms. The behavior of the free stator was analyzed using the ATILA finite element software. Torque vs. speed relationship was measured from the transient speed change with a motor load. A starting torque of 17 muNm was obtained at 20 Vrms. The main features of this motor are low cost and easy assembly because of a simple structure and small number of components.     

Formation studies of TiC from carbon coated TiO2

This paper deals with the formation of titanium carbide from carbon coated titanium dioxide precursors. This study makes use of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and both scanning and transmission electron microscopy (SEM and TEM). DSC curves of both coated and mixed 33.2 wt % carbon containing titania demonstrates the superiority of the coated precursor by exhibiting both more reactions and reactions at lower temperatures than the mixed powder. Weight loss as powders were reacted in argon at varying temperatures was measured using TGA, while heat flow vs. temperature was measured by DSC. The weight loss allowed for calculation of the activation energy of TiC via the formation of various lower oxides of titanium. The activation energy was calculated as 731.6 ± 24.2 kJ/mol. XRD was used to characterize the products resulting from the reaction of the carbon coated precursor at isotherms at each 100 °C interval from 1100 to 1500 °C, inclusive. These diffraction patterns support the hypothesis that the TiC formation proceeds through the formation of lower oxidation states of titanium.     

Sintering properties of submicron TiC powders from carbon coated titania precursor

The sintering behavior of submicron titanium carbide (TiC) synthesized from carbon coated titania (TiO₂) precursor was investigated in TiC-Ni system. The densification was examined as functions of initial carbon content (30.95–34 wt.%) and Ni content (3–20 wt.%). The sintered density of TiC-Ni was markedly decreased with increased carbon content in the precursor. The amount of Ni had a relatively small influence on the densification of submicron TiC-Ni cermet compared with TiC (commercially available HCS)-Ni cermets. The results show that submicron TiC with only 3 wt.% Ni can be sintered to densities above 95% TD in flowing Ar+10H₂ at 1500°C and below. The improvements in densification result from the capillary force increase since it is inversely dependent on the particle size. With decreased Ni content, the Vickers hardness increased and the fracture toughness decreased, as expected. However, the sufficient densification cannot be achieved for commercial HCS TiC powder sintered with Ni (<10 wt.%) under the same conditions. Therefore, both the Vickers hardness and fracture toughness decreased as the Ni content decreased. This was due to the increase of porosity in the sintered samples containing commercial TiC powder.     

Removal of ammonium ion from aqueous solution using natural Turkish clinoptilolite

A study on ion exchange kinetics and equilibrium isotherms of ammonium ion on natural Turkish clinoptilolite (zeolite) was conducted using a batch experiment technique. The effects of relevant parameters, such as temperature, contact time and initial ammonium (NH(4)(+)) concentration were examined, respectively. The pseudo first-order, pseudo second-order kinetic models and intraparticle diffusion model were used to describe the kinetic data. The pseudo second-order kinetic model provided excellent kinetic data fitting (R(2)>0.990) and intraparticle diffusion effects ammonium uptake. The Langmuir and Freundlich models were applied to describe the equilibrium isotherms for ammonium uptake and the Langmuir model agrees very well with experimental data. Thermodynamic parameters such as change in free energy (DeltaG(0)), enthalpy (DeltaH(0)) and entropy (DeltaS(0)) were also determined. An examination of the thermodynamic parameters shows that the exchange of ammonium ion by clinoptilolite is a process occurring spontaneously and physical in nature at ambient conditions (25 degrees C). The process is also found to be exothermic. The results indicate that there is a significant potential for the natural Turkish clinoptilolite as an adsorbent material for ammonium removal from aqueous solutions.     

Synthesis of Submicrometer Titanium Carbide Powders

A novel synthesis process, based on a carbothermal reduction of titania, has been developed for producing high–purity, submicrometer, and nonagglomerated titanium carbide powders. The process utilizes a carbothermic reduction reaction of novel coated precursor powders that has potential as a high–quality (submicrometer and high–purity) powder synthesis route. The precursor is derived from a titania (TiO₂) and a hydrocarbon (C₃H₆) gas and provides high contact area between the reactants. This yields a better distribution of carbon within the titania and inhibits the agglomeration among the titania particles, resulting in a more complete reaction and a purer product at a comparatively low temperature. The TiC powders produced at 1550°C for 4 h under argon gas flow have oxygen content of 0.6 wt% and total carbon content of 22.9 wt%, a very fine particle size (,0.1μm) (surface area of about 20 m²/g), uniform shape, and loose agglomeration.