Effect of TiO2 additions on densification and mechanical properties of new mulltifunction resistant porcelains using economic raw materials

The aim of this work is to determine the effect of TiO₂ on sintering and mechanical proprieties of new multifunction resistant (MFR) porcelain prepared from local abundant raw materials. Based on a preliminary work, the new selected composition was 30 wt% kaolins (20 wt% kaolin halloysite type + 10 wt% kaolin Tamazart), 45 wt% k-feldspar and 25 wt% quartz and containing different contents of TiO₂ (3, 5 and 8 wt%). The sintering temperatures of mixtures were between 1140 and 1260 °C. Subsequently, the obtained phases in the elaborated samples were investigated by X-ray diffraction and Fourier transform infrared spectroscopy analyses, Raman spectroscopy and SEM analysis. The optimum sintering conditions gave a higher bulk density (2.47 g.cm⁻³) and excellent mechanical properties: The three point flexural strength (3PFS), Vickers micro-hardness (VMH) and apparent porosity (P_A) of porcelains sintered at 1160 °C were 238 MPa, 12.3 GPa and 2%, respectively. This obtained 3PFS value is drastically higher than that achieved for conventional porcelains (ranged between 60 and 80 MPa). Moreover, these two best 3PFS (238 MPa) and VMH (12.3 GPa) values achieved for this new MFR porcelains were considerably higher when compared to those values (3PFS=218 MPa and VMH=6.5 GPa) obtained by others for porcelain −30% ZrO₂ composite, even though their mixtures were hot pressed in vacuum at 970 °C for 2 min. Besides, the maximum value achieved for the new MFR porcelains is nearby that of the flexural strength of porcelain containing 5 wt% TiO₂ and 30 wt % alumina (about 240 MPa). In other words, the presence of 30 wt % alumina in their product well confirm the benefic effect of the used raw materials (saving 30 wt % alumina) on porcelain strengthening.     

Comparison of conventional Knoop and Vickers hardness of ceramic materials

Ceramics generally have a lower Knoop than Vickers hardness. This difference is due to the elastic recovery occurring around a Knoop indentation and the difference in representative area considered to calculate the hardness value.Conventional hardness tests with Knoop and Vickers indenters were performed in order to show how Knoop hardness test can give the same hardness number obtained by Vickers hardness test. This is obtained when Knoop hardness number is calculated based on the residual plastically deformed area whether projected or true. Complementary hardness data obtained from the literature were used in this work in order to validate the method proposed in this work. A revision of the well-known relation of Marshall is proposed in order to determine the elastic modulus by means of one Knoop hardness test when the Vickers hardness is unknown.     

The effects of the size of nanocrystalline materials on their thermodynamic and mechanical properties

This work has considered the intrinsic influence of bond energy on the macroscopic, thermodynamic, and mechanical properties of crystalline materials. A general criterion is proposed to evaluate the properties of nanocrystalline materials. The interrelation between the thermodynamic and mechanical properties of nanomaterials is presented and the relationship between the variation of these properties and the size of the nanomaterials is explained. The results of our work agree well with thermodynamics, molecular dynamics simulations, and experimental results. This method is of significance in investigating the size effects of nanomaterials and provides a new approach for studying their thermodynamic and mechanical properties.     

Formation mechanism and microhardness characterization of the ultrasonic hardening layer in cementitious materials

Ultrasonic surface treatment (UST) is a novel treatment method to improve the durability of cementitious materials, resulting in the formation of an ultrasonic hardening layer (UHL). The UHL acts as an effective natural coating, offering penetration and erosion protection. However, the formation mechanism and the quantitative characterization of the UHL have not been studied, and the validity of the UST on the top and side surfaces of cementitious materials is still unknown. Therefore, in this study, we investigated and proposed a formation mechanism for the UHL, and defined a transition layer between the UHL and the matrix. We also utilized HV microhardness testing to provide an effective quantitative characterization method for the UHL. Finally, using a set of custom-designed ultrasonic molds, we confirmed the validity of the UST on the top and side surfaces of the cementitious materials.     

Comparison of theoretical and experimental microhardness of tetrahedral binary Zn1-xErxO semiconductor polycrystalline nanoparticles

${\mathrm{Zn}}_{1?\mathrm{x}}{\mathrm{Er}}_{\mathrm{x}}\mathrm{O}$ polycrystalline nanoparticles with various compositions $(x=0.01,0.02,0.03,0.04,0.05,$ and $0.10)$were prepared using sol–gel techniques, for which zinc acetate dihydrate and erbium 2–4 pentanedionate are used as precursors. Nanoparticles were pressed under a pressure of $4$?tons for $5$?min into disk-shaped compacts with 2?mm thicknesses and 10?mm diameters. The pressed samples were annealed at 400?°C for $30$?min. X-ray diffraction (XRD), scanning electron microscopy (SEM), and Vickers microhardness analyses of the produced Er-doped $\mathrm{ZnO}$ bulk nanomaterials were performed. Specifically, in this study we focused on the analysis of their mechanical properties. Undoped and Er-doped bulk samples were investigated according to Meyer's law; the proportional sample resistance (PSR), elastic/plastic deformation (EPD), and indentation-induced cracking (IIC) models; and the Hays–Kendal (HK) approach. As a result, the IIC model was more suitable to determine the micromechanical properties and the reverse indentation size effect ($\mathrm{R}\mathrm{ISE}$) behavior of Er-doped $\mathrm{ZnO}$ semiconductors.     

A reliable technique to determine the local mechanical properties at the nanoscale for cementitious materials

A Hysitron Triboindenter has been used to determine the mechanical properties of hardened cement paste and cement paste at the early age. This technique provides an in-situ scanning probe microscopy (SPM) imaging facility that allows pre and post-test observation of the sample. The same probe is used to indent and image eliminating the complicated situation of locating the same area with different instruments or coupling two different instruments, such as a SEM and a nanoindenter to work together. This paper presents preliminary results of experiments performed on hardened cement paste and cement paste at the early age.     

On the linear correlation between microhardness and mechanical properties in polar polymers and blends

The tensile elastic modulus (E), yield stress (σ_Y) and microhardness (MH) of neat and binary and ternary blends of glassy semicrystalline ethylene–vinyl alcohol copolymer (EVOH), a glassy amorphous polyamide and a semicrystalline nylon‐containing ionomer covering a broad range of properties were examined. The tests were carried out on dry and water‐equilibrated samples to produce stiffer and softer materials, respectively. From the results, more accurate linear correlations were found to describe adequately the microhardness, modulus and yield stress of these strongly self‐associated polymers through hydrogen bonding. Copyright © 2003 Society of Chemical Industry     

Microscopic regulation of plant morphological pores on mechanical properties of porous mullite materials

Generally, a multilayer structure is present inside a walnut shell, and the residual structure of the walnut shell is retained after impregnation and firing. When the walnut shell is used as a pore-forming agent, this structure helps in improving the mechanical and thermal insulation properties of the lightweight porous materials. In this study, porous mullite materials (PMMs) with plant morphological structure pores were prepared using a-Al₂O₃ and silica powder as the raw materials with addition of sol-impregnated walnut shell powder (WSP). The influence of sol type and firing temperature on the pore structure of the PMMs was analyzed, which affected the compressive strength and thermal conductivity. The plant morphological porous structure was observed in the samples after sol impregnation. After firing at different temperatures, the porous structure gradually contracted and supported the pores, improving the mechanical properties, while the complex porous structure increased the heat conduction path, thereby improving the insulation performance. Using WSP impregnated with silica-sol and zirconia-sol as pore-forming agents, PMMs with higher compressive strength and relatively low thermal conductivity (TC) were prepared.     

Relationships between synthesis and mechanical properties of new polyurea materials

New segmented polyureas were prepared from 4,4′-diisocyanato dicyclohexylmethane and amino terminated polyoxypropylene. Different cycloaliphatic and aromatic diamines were used as chain extenders as well as to synthesize the corresponding model hard segments (HSs). The competition between polycondensation and HS crystallization requires a sufficiently fast reaction (e.g., cycloaliphatic diamines associated with a catalyst, if necessary in solution), although low reactivity monomers would be necessary to avoid demanding processing techniques such as reaction injection molding; otherwise, materials with isolated (i.e., not chemically linked) HS are obtained and they display poor mechanical properties. In contrast, when an appropriate synthesis procedure is used, elastomers with high molar masses and narrow molar mass distributions can be obtained. These characteristics, associated with the high melting temperature of the hard domains, result in very good mechanical behavior, up to high enough temperatures (∼ 180–190°C). The presence of low molar masses can be responsible for a rather low but continuous energy dissipation between the relaxations of the soft and hard domains (and particularly at room temperature), but can be well limited by a short thermal treatment at high temperature. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2265–2280, 1997     

Structural and biological properties of novel Vanadium and Strontium co-doped HAp for tissue engineering applications

The development of novel bioactive materials with improved physical and biological properties is crucial for advancing tissue engineering applications. In this study, we synthesized a Vanadium and Strontium co-doped hydroxyapatite (V–Sr:HAp) nanoparticle intending to enhance the performance of pure HAp. The V–Sr:HAp nanoparticles were synthesized using a microwave-assisted reflux condensation method, and their structural and chemical characteristics were investigated using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The morphology and elemental composition of the nanoparticles were examined through scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). The XRD analysis confirmed the presence of characteristic peaks of HAp in each sample. SEM images revealed well-connected and highly agglomerated small sphere-like morphology in both pure HAp and V–Sr:HAp nanoparticles. The Vickers hardness test demonstrated the improved mechanical strength in V–Sr:HAp compared to pure HAp. Antibacterial efficacy was evaluated using an agar diffusion test, which showed enhanced antibacterial activity in the co-doped HAp samples against S. aureus and P. aeruginosa. Moreover, the Ca–P deposition rate on the surface of the co-doped HAp samples during biomineralization was higher. Hemolysis assay results have indicated compatibility of both pure HAp and V–Sr:HAp with human blood (<5% lysis). The results of cell viability tests demonstrate that the V and Sr co-doped HAp samples do not exhibit any cytotoxic effects and instead promote cell proliferation. Overall, the incorporation of V and Sr metal ions into HAp presents a promising bio-functional tool for tissue engineering applications, offering improved mechanical and antibacterial properties.     

Effect of c-BN surface modification on the microstructure and mechanical properties of (Ti,W)C-based cermet tool materials

Alumina-coated cubic boron nitride (c-BN) particles (c-BN@Al₂O₃) were prepared using a heterogeneous nucleation method. Then, they were added to a (Ti,W)C-based cermet tool material after synthesis via vacuum hot-press sintering. The microstructure and mechanical properties of the (Ti,W)C-based cermet tool material with varying c-BN@Al₂O₃ contents were recorded and analyzed. The results show that with increasing c-BN@Al2O3 concentration, the relative density, flexural strength, fracture toughness, and Vickers hardness all increase first and then decrease, and the average grain size first decreases and then increases. The introduction of Al₂O₃ into the c-BN particles used for surface modification can improve the wettability and interfacial bonding strength between the c-BN and matrix particles, restrain the grain growth of the matrix particles, and improve the flexural strength of cermet tool materials. The addition of c-BN@Al₂O₃ also alters the crack propagation mechanism of the cermet tool material and introduces multiple toughening mechanisms to improve the fracture toughness of the cermet tool material. The high hardness of c-BN and Al₂O₃ is the main reason for the increase in hardness; however, excessive addition of such material reduces the relative density, resulting in a decrease in hardness.     

Improving the microstructural and mechanical properties of in-situ zirconia-mullite composites by optimizing the simultaneous effect of mechanical activation and additives

The current study aims to investigate the microstructural properties, diametral tensile strength, Weibull modulus, and surface roughness (Ra) of the zirconia-mullite composites. The simultaneous effect of duration of the mechanical activation (MA) process of starting materials, as well as TiO₂ and ZnO additions on the mentioned properties, were studied. X-ray diffraction analysis showed that mullite was the main crystalline phase in 6–24 h mechanically activated-TiO₂ containing samples which were subsequently heat treated at 1450 °C. Prolonging the duration of the MA process to 72 h led to the crystallization of the tetragonal zirconia as one of the main crystalline phase in the mentioned samples. As the heat treatment temperature increased to 1550 °C, the dependence of the type of the crystalline phases on the milling time eliminated and mullite became the main crystalline phase in 6–72 h MA processed samples. The transformation of starting materials to mullite and t-zirconia was not progressed effectively in ZnO containing samples which were heat treated at 1450 °C. However, by increasing the temperature of the heat treatment process to 1550 °C, both mullite and zirconia were efficiently crystallized in 6–72 h MA processed ZnO containing ones. Scanning electron microscopy results revealed that prolonging the duration of the milling process of the additive containing mixtures from 6 to 72 h could eliminate the acicular morphology of the mullite phase. 72 h mechanically activated ZnO containing sample which was later heat-treated at 1550 °C had the highest noticeable diametral tensile strength of 270 ± 15 MPa. The Weibull modulus of composite samples increased from 10.07 to 12.37 and 20.95 by the addition of TiO₂ and ZnO to the starting mixture, respectively. Finally, it was found that prolonging the milling time increased the Weibull modulus remarkably and decreased the Ra values as a result of the homogeneity development in the composite samples.     

Evaluation of effects of non-thermal plasma treatment on surface properties of CAD/CAM materials

The purpose of this in vitro study was to evaluate the effect of the non-thermal plasma (NTP) treatment on the wettability and surface roughness of different types of CAD/CAM materials as well as the shear bond strength (SBS) of adhesive resin cement to the treated surfaces. Three different materials, namely; resin nano ceramic, feldspathic ceramic and poly(methyl methacrylate) (PMMA)-based samples were treated with NTP for different time points to evaluate the effect of NTP treatment on the surface properties of CAD/CAM materials. Moreover, surfaces of CAD/CAM materials were visualised with scanning electron microscopy (SEM). A 90-second NTP treatment time was determined as the optimum time for the highest measured wettability, and thus, the 90-second NTP treated samples were used for the SBS test and evaluation of the failure types. Our results revealed the NTP treatment lowered the contact angles and increased the roughness of all tested materials. Moreover, The NTP treatment significantly enhanced the SBS of resin nano ceramic and feldspathic ceramic-based materials. NTP could be considered as a novel pre-treatment method to improve surface properties and the bonding performance of ceramic-based CAD/CAM materials.     

Frontal curing of epoxy resins: Comparison of mechanical and thermal properties to batch-cured materials

The epoxy resin diglycidyl ether of bisphenol F (DGEBF) was cured by the aliphatic amine curing agent Epicure 3371 in a stoichiometric ratio both frontally and in a batch-cure schedule. Glass transition temperatures (T_g) were determined using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). DMA also was used for studying the storage modulus (E′) and tan delta (tan δ) of the cured samples. Tensile properties of epoxy samples were tested according to ASTM D638M-93. The properties of the frontally cured epoxy resin were found to be very close to that of batch-cured epoxy resin. Velocity of cure-front propagation was measured for both neat and filled epoxy. Rubber particles (ground tires) were used as a filler. The maximum percentage of filler in the epoxy resin allowing propagation was 30%. Because of convection, only descending fronts would propagate. Advantages and disadvantages of frontal curing of epoxy resins are discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1209–1216, 1997     

Phase composition,microstructure, and mechanical properties of polymer-derived SiOC glass-ceramics reinforced by WC particles

In this work, a tungsten carbide (WC)-containing silicon oxycarbide (SiOC) glass-ceramic was prepared from WC-filled polysiloxane via pyrolysis and subsequent spark plasma sintering (SPS). The sintering behavior of SiOC was investigated by monitoring the densification temperature and shrinkage displacement. The phase composition and microstructure of ceramics were characterized by using FTIR, XRD, SEM, Raman spectrum, and optical microscope. It was shown that upon increasing the sintering temperature from 1400 °C to 1600 °C, the densification of ceramics was further improved, and the disorder of free carbon in SiOC was linearly decreased with sintering temperature. In addition, it was found that the incorporation of WC particles was effective to reinforce the mechanical properties of ceramics, and relevant strengthening mechanisms were discussed here. Finally, a correlation between phase composition, microstructure, and macroscopic performances of SiOC glass-ceramics was successfully derived.     

Enhanced mechanical and thermal properties of nanodiamond reinforced low density polyethylene nanocomposites

In this study, the reinforcement effects of low-content hydrophilic nanodiamond (ND) on linear low-density polyethylene (PE) nanocomposites were investigated. ND was incorporated in PE via simple solution blending. The obtained PE/ND nanocomposites were characterized using scanning electron microscopy, ultraviolet–visible spectra, X-ray diffraction, tensile test, thermogravimetry, and differential scanning calorimetry. Generally, PE/ND nanocomposites with poor interfacial interaction cause large agglomerates, resulting in brittle and poor mechanical properties. Owing to the different natures of non-polar PE and polar ND, the higher the ND content, the larger the agglomerates formed in the nanocomposites. However, PE/ND nanocomposites show unique mechanical properties, that is, the Young's modulus, tensile strength, elongation at break, and toughness increased upon the incorporation of ND. The Young's modulus of the PE/ND nanocomposites exceeded the theoretical value calculated using the Halpin–Tsai model. In addition, the toughness increased by 18% at only 0.5 wt% ND loading. Furthermore, there was an increase in the thermal degradation temperature, melting temperature, and crystallization temperature.     

Effect of diamond addition on microstructure and mechanical properties of Ti(C,N)-based cermets

This study explored the effect of diamond content (0, 0.3, 0.6, and 0.9 wt%) onTi(C_0.5,N_0.5)-based cermets prepared via vacuum sintering with respect to their final mechanical properties and microstructures, characterized using X-ray diffractionand scanning electron microscopy. After liquid phase sintering, all cermets exhibited a ‘black core/grey rim'and partial ‘white core/grey rim'structure. The cermet with 0.6 wt% diamond exhibited optimal mechanical properties with a Vickers hardness of 1795 ± 32 H V, transverse rupture strength of 2026 ± 45 MPa, and plane strain fracture toughness of 12.95 ± 0.3 MPa m^1/2. This is due to grain refinement and the uniformly distributed ‘white core/grey rim'grains. During the incipient liquid formation stage,a higher carbon activity arising due to diamond graphitization may shift the equilibrium towards the product, thereby yielding additional white cores due to the consumption of heavy elements in the binder. Excessive diamond introduction inhibited the dissolution of Ti(C_0.5,N_0.5) into the binder, resulting in fewer white cores.     

Epoxy networks for medicine applications: Mechanical properties and in vitro biological properties

This work describes the physicochemical, mechanical, and in vitro biological properties of three epoxy networks based on diglycidyl ether of bisphenol‐A (DGEBA) epoxy prepolymer cured with triethylenetetramine, 1‐(2‐aminoethyl)piperazine (AEP) and isophoronediamine. The mechanical properties were evaluated with respect to impact and flexural tests. Functionality rules the mechanical behavior of epoxy networks by increasing the crosslink density and the flexural modulus, increasing T_g and decreasing the chain flexibility and the impact resistance. The biological interactions between the obtained epoxy polymers and blood were studied by in vitro methods. Studies on the protein adsorption, platelet adhesion, and thrombus formation are presented. The protein adsorption assays onto polymeric surfaces showed that the epoxy networks adsorbed more albumin than fibrinogen. The results about platelet adhesion and thrombus formation indicated that DGEBA‐IPD and DGEBA‐AEP networks exhibits good hemocompatible behavior. The materials revealed no signs of cytotoxicity to Chinese hamster ovary cells, showing a satisfactory cytocompatibility. In this way, we can assume that the epoxy polymers are biocompatible materials. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The compaction and mechanical properties of agglomerated materials

Following a discussion of the stages of powder compaction as presented in the literature, the authors propose extension of the generally accepted two stage compaction process to a four stage process for agglomerated materials. The mechanisms of compaction for two different spray-dried ceramic powders, a wall-tile granulate, and a ferrite granulate are described. After an adaptation of the compaction formulae of Kawakita for the highly porous spray-dried granulates a set of equations with a better fit is given, describing the relationships between pressure and volume compaction or density, and between porosity and strength and modulus of elasticity. All proposed equations are closely related to Kawakita's empirical equation and the theoretical relationship of Hasselman, and give an accurate fit over the whole range of pressures.