bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of Young's Modulus of Hydroxyapatite Doped with Magnesium by Vibration Method
Authors: Suciu Oana , Bereteu Liviu , Drăgănescu Gheorghe , Ioanovici Teodora
Published: March 2014

Implants and bone reconstruction have known a great development recently. Synthesized bone tissues must have mechanical, physiological and biological properties closer to natural bone, as much as possible. Bioceramics are materials which fulfill these conditions, being biocompatible with mechanical strength similar to bone. One material widely used is hydroxyapatite. Hydroxyapatite is slightly different from bone tissue and it forms the mineral part of bone tissue. In order to improve mechanical properties and biological compatibility hydroxyapatite is doped with different compounds, mainly chemical elements. Magnesium, a chemical element present in human bone structure is one of these compounds.
Virtual Geometric Model of the Human Lower Limb
Authors: Rusu Lucian , Toth-Taşcău Mirela , Toader-Pasti Cristian
Published: March 2014

The aim of this paper is to develop and validate the mathematical model of the human lower limb based on Denavit-Hartenberg (D-H) robotics convention. The proposed geometric model has 7 degrees of freedom (DOF) (3 DOF in hip joint, 2 DOF in knee joint, and 2 DOF in ankle joint). The fixed reference system was placed in the weight centre of the human body. The input data for the model are the angle variations and anthropometric parameters of the lower limb. The angle variations can be defined or imported from a gait analysis system. The anthropometric parameters were introduced from the literature. The model can be adapted to both left and right lower limb. The geometric model was solved in MATLAB environment. The model validation was individually realized taking into account the normal range of motion (ROM) of each joint.
Vibrated Concrete vs. Self-Compacting Concrete: Comparison of Fracture Mechanics Properties
Authors: Korte Sara , Boel Veerle , de Corte Wouter , de Schutter Geert
Published: March 2014

This study focuses on the fracture mechanics aspect of self-compacting concrete, compared to vibrated concrete. The most commonly used experiments to investigate the toughness and cracking behaviour of concrete are the three-point bending test (3PBT) on small, notched beams, and the wedge-splitting test (WST) on cubic samples with guiding groove and starter notch. From the resulting P-CMOD curves (applied load versus crack mouth opening displacement), different fracture parameters, such as fracture energy and fracture toughness, can be extracted. Moreover, using inverse analysis, the σ-w relationship (tensile stress versus crack width) can be derived. This paper lists the results of a series of tests on samples, made of VC, SCC of equal strength, and SCC with identical w/c factor. Subsequently, a comparison of the mechanical characteristics is made, revealing important differences regarding several fracture parameters.
Dynamic Testing of a Reinforced Concrete Road Bridge
Authors: Ghindea Cristian Lucian , Racanel Ionut Radu , Cruciat Radu
Published: March 2014

Considering on one hand the calculation model of the bridge, simplifying assumptions and design criteria and on the other hand the inherent differences between the project and final structure, the real structure behaviour under traffic loads can be different from that one considered in the design stage. Therefore the need of experimental tests before commissioning of bridges arises and this task is generally conditioned by complexity of the structure, the technologies used in construction and the requirements of the relevant stakeholders. The paper presents the test conditions for a reinforced concrete road bridge in Romania and the results obtained following the experimental tests. The experimentally determined dynamic characteristics of the bridge and the peek vertical accelerations are compared with those obtained by performing numerical analyses of the bridge. Due to the fact that the bridge is provided with walkways, it is appropriate to presume that the vibrations induced by road traffic will affect the pedestrians walking on the bridge. Same experimental data presented above can provide a view into how traffic induced vibrations can affect pedestrians on the bridge. For this reason, in the paper are presented the results in terms of human perception and the comparison between the resulting values and some generally accepted values
Steels as Materials for Sonotrode Tools
Authors: Kováčik Jaroslav , Emmer Štefan
Published: March 2014

The investigation of suitable steels for sonotrode tool applications was performed. In this case in addition to good sonotrode properties (good transmission of ultrasonic energy, resistance to gigacycle fatigue) the material ought to meet also the tool properties (high hardness and wear resistance). The study was focused on tool steels, which are relatively cheaper than the currently best sonotrode tool material FerroTitanit cermet, and better than usual sonotrode materials AW 7075 aluminum alloy and titanium alloy Ti6Al4V. The suitability of steels for this purpose was evaluated by measuring the ultrasound energy transmission at a frequency of 30 kHz.
Experimental Case Studies on Clay Fired Bricks Compressive Strength
Authors: Suciu Ovidiu , Cruciat Radu , Ghindea Cristian Lucian
Published: March 2014

Modern age manufacture technology requires controlled conditions for the burning and pressing of the clay bricks, while in the past these aspects weren't strictly controlled. It is expected to have different behaviours of the brick units for existing masonry buildings, as a result of the diverse fabrication technologies at different moments in time.
The present paper presents a case study about the experimental testing on two batches of clay fired bricks. First batch is obtained from an existing structures and the second batch is represented by new bricks. Compression tests were conducted on specimens extracted from every batch of bricks. The experimental tests were carried out according to the current national standard for masonry units. For every tested batch of bricks, the standardized compression strength was computed as an arithmetic mean of the corrected ultimate stress. Following the large dispersion of the results for the specimens obtained from old bricks, the authors consider the standard method to determine the compressive strength of the bricks isn’t suitable for the determination of the brick batch class. Therefore, a series of probabilistic calculation were conducted by the assimilation of the experimental tests results to the processing methods characteristic for masonry. Using these procedures, the characteristic and the 5% fractile value of the compressive strength were determined for every batch of masonry units.
Experimental Testing of a Base Isolated Model in Laboratory Conditions
Authors: Cruciat Radu , Ghindea Cristian Lucian
Published: March 2014

A method used world-wide to reduce the effects of seismic motion it is represented by the base isolation of the structure. The application of this method aims to an increase of the base flexibility in the horizontal plane. In order to illustrate the advantages of the base isolation system an experimental analysis in frequency domain was achieved. The test specimen was represented by a small scale model of a simple structure. Frequency domain analysis has allowed a comparison between the response of the structure with and without base isolation. The comparison pointed the positive effect of base isolation in order to reduce the resonant response of the fixed base structure. In order to validate the experimental results and to extrapolate response to cases closer to real isolation systems, finite element models of the structure with and without isolated base were made. The numerical models were calibrated with experimental models in terms of natural vibration period and damping ratio and they were designed to describe the real experiments, as far as possible. Comparative response analysis of the two models has allowed experimental data validation and the numerical model acceptance. The average error between the two response curves in the frequency domain was considered acceptable, taking into account the general precision of an experimental test. In order to fill some gaps due to boundary conditions of the experiment a finite elements analysis was performed to extrapolate the response of the isolated structure for higher values of the damping ratio at the base isolation system level and for random seismic motion.
Influence of Cracks on Chloride Penetration in Mortar Specimens Subjected to Cyclic Treatment
Authors: Sosdean Corina , Marsavina Liviu , de Schutter Geert
Published: March 2014

Chloride-induced steel corrosion is worldwide one of the major causes of deterioration of reinforced concrete structures, producing loss of structural strength and stability. One of the most aggressive exposure conditions for concrete is marine environment together with the drying and wetting conditions by tidal and splash action. In such an aggressive environment the presence of cracks has a great influence on chloride ingress.In this paper both the experimental and the numerical results of the influence of artificial cracks on chloride penetration in mortar specimens are presented. The experimental results were obtained using chloride penetration tests on mortar specimens of different sizes, with and without artificial cracks, subjected to a cyclic treatment. Numerical results were obtained using transient finite element analysis by simulating chloride mass diffusionwith COSMOS/FFE realized with the heat transfer modulus T, which was replaced by the total concentration C, and the thermal conductivity Kx, replaced by diffusion coefficient D. Comparisons between the results on chloride penetration concluded that the numerical ones obtained using the mass transfer modulus agree fairly well with the experimental ones. In addition the influence of crack length on chloride ingress was presented.
On-Site Experimental Testing to Study the Vibration of Composite Floors
Authors: Ghindea Cristian Lucian , Cretu Dan , Popescu Monica , Cruciat Radu , Tulei Elena
Published: March 2014

As a general trend, in order to reduce material consumption or to reduce the mass of the structures, composite floor slabs solutions are used to achieve large spans floor slabs. This solutions led to floors sensitive to vibrations induced generally by human activities. As a verification of the design concepts of the composite floors, usually, it is recommended a further examination of the floor after completion by experimental tests. Although the experimental values of the dynamic response of the floor are uniquely determined, the processing can take two directions of evaluation. The first direction consist in determining the dynamic characteristics of the floor and their comparison with the design values. Another way that can be followed in the processing of the experimental results is to consider the human perception and comfort to the vibration on floors. The paper aims to present a case study on a composite floor, with steel beams and concrete slab, tested on-site. Both aspects of data processing are analyzed, in terms of the structural element, and in terms of the effect on human perception and comfort. Experimentally obtained values for the dynamic characteristics of the floor are compared with numerical values from finite element analysis, while the second type of characteristic values are compared with various human comfort threshold values found in international standards.
Uniaxial Compression Tests of Metallic Foams: A Recipe
Authors: Kováčik Jaroslav , Marsavina Liviu , Adamčíková A. , Simančík F. , Florek R. , Nosko M. , Tobolka P. , Minár P. , Mináriková N. , Jerz J. , Linul E.
Published: March 2014

In case of metallic foams the stress-strain curve observed during uniaxial compression is often not smooth, expecting plateau is often missing, and the curve instead of slowly increasing stress before final densification takes place often exhibit a lot of peaks with even local stress drops. It is generally accepted that the origin of this behavior is linked to the heterogeneity and/or anisotropy of foams, ductility or brittleness of used matrix alloy and the presence of surface skin. This contribution is designed as a recipe for metal foam investigator how to handle the uniaxial compression test results on metallic foams. Aim of this contribution is to introduce engineers and researchers also to the unusual events that can occur during foam compression test.
Evaluation of Thermal Stresses in Sandwich Panels with Chiral Cellular Cores
Authors: Sorohan Stefan , Constantinescu Dan Mihai , Sandu Marin , Sandu Adriana
Published: March 2014

Sandwich panels are important components of advanced structures used in aerospace, automotive, railway, civil engineering etc. They are subjected to high and repeated variations of temperature which induce additional stresses as the core and the face sheets are from different materials having different coefficients of thermal expansion and moduli of elasticity. Therefore it is important to evaluate both mechanical and thermal stresses. In the literature one can find thermo-mechanical analyses of sandwich panels with metallic or composite face sheets and having a honeycomb or compact core made from polyurethane foam. In this paper was analysed a plane sandwich panel made from a cellular rigid polyurethane core, having a chiral configuration and auxetic properties (negative Poissons ratio) exposed to a stationary temperature field with a linear variation from +25 °C on one sheet to-50 °C on the opposite sheet. Two boundary conditions were considered in the thermo-mechanical evaluation: the free panel and the panel simply supported around the edges.
Analysis of Deformation Bands in Polyurethane Foams
Authors: Apostol Dragos Alexandru , Constantinescu Dan Mihai , Marsavina Liviu , Linul Emanoil
Published: March 2014

Closed cell polyurethane foams with densities of 100, 160 and 301 kg/m3 were tested in compression at speeds of 1 and 5 mm/min. Digital image correlation (DIC) is used to determine the engineering characteristic curve, modulus of elasticity, Poisson's ratio and the deformation bands that appear during deformation and prior to the final failure of the specimens. By using this procedure both global and local phenomena are observed and analyzed. While each specimen is compressed the damage behaviour of the foams is directly observed in different stages, as being in the linear elastic domain, in the plateau region, and in the densification region. Several observations, characteristic for each foam density are discussed. As damage mechanisms are different, DIC allows the direct monitoring of the formation of the deformation bands and their propagation till the final failure of the foams, as long as calculations of the local strains are possible. Maps of the vertical displacements and local Mises strains are presented and comments on the characteristics of the deformation bands are done.
Experimental Determination of Mechanical Properties of Aluminium Foams Using Digital Image Correlation
Authors: Voiconi Tudor , Linul Emanoil , Marsavina Liviu , Kováčik Jaroslav , Kneć Marcin
Published: March 2014

This paper presents an experimental characterization of three different types of closed-cell aluminium alloy foams (AlMg1Si0.6, AlSi12Mg0.6 and AlMg0.6Si0.3) under static compressive loading. This study was carried out on half-cylindrical specimens with skin. The influence of foam density on compressive behaviour was investigated for densities ranging from 430 kg/m3 to 935 kg/m3. The compression tests were performed at room temperature (23°C) with a constant crosshead speed of 0.5 mm/min. Strain distribution, yield stress and compressive modulus values were recorded using Digital Image Correlation. Experimental results show that the mechanical properties (Youngs Modulus, yield stress and plateau stress) increase with density.
Flexural Properties of Polyamides: Influence of Strain Rate, Friction and Moulding-Induced Anisotropy
Authors: Serban Dan Andrei , Voiconi Tudor , Marsavina Liviu , Silberschmidt Vadim V.
Published: March 2014

In recent years, advances in material testing equipment caused the determination of mechanical properties by means of three-point bending tests to lose ground in detriment to more accurate tensile tests. However, if components undergo bending deformation in service, the identification of the materials flexural behaviour is essential. The investigated material is a thermoplastic polymer, test specimens being cut in prismatic shapes from injected sheets, which present a variation in properties due to cooling conditions. This paper presents results of three-point bending tests with emphasis on the influence of strain rate and anisotropy on flexural strength and chord modulus. Results show an increase in flexural properties with strain rate and a considerable influence of anisotropy on mechanical properties.
Measurement of Thermoplastics Tensile Proprieties Using Digital Image Correlation
Authors: Dudescu Cristian , Botean Adrian , Hărdău Mihail , Bal Nicolaie
Published: March 2014

This paper presents measurement of tensile proprieties of thermoplastics by digital image correlation method. The objectives are to characterize based on experimental data the pre-and post-yield regime of polyvinylchloride (PVC) under uniaxial tension and to investigate the rate-dependent large deformation behaviour over crosshead speeds of 1, 5 and 25 mm/min respectively. The true strain-stress curves of PVC tested with different loading speeds are experimentally obtained and based on these a phenomenological constitutive model is implemented. The theoretical material model considers the variation of strain rates due to the inhomogeneous deformation behaviour of thermoplastic polymer and includes six parameters (material constants) to be identified according to the experimental results. It can be found that the effect of the strain rate on the true stress strain curves is small for lower strain rates but cannot be ignored for higher strain rate.
Deflection Determination of V-Beam Thermal Sensors Using Digital Image Correlation
Authors: Chiorean Radu , Dudescu Cristian , Pustan Marius , Hărdău Mihail
Published: March 2014

The purpose of this paper is to present some results and benefits for using the 2D Digital Image Correlation (DIC) method on the deflection determination of the V-beam thermal sensor. Therefore, the influence of the main geometrical parameters of the V-beam type thermal sensors on its deflection is evaluated. An experimental set-up was designed is order to acquire high resolution images of the deformed sensor at different temperatures. The analytical and the finite element (FE) studies that were performed on theoretical models of the V-beam sensor led to the validation of the experimental results and thus to the validation of the method.
Measurement and Analysis of Noise Generated in a Tram Rail Wheel Contact
Authors: Ungureanu Alexandru Catalin , Bereteu Liviu , Tocarciuc Alexandru , Nagy Ramona , Simoiu Dorin
Published: March 2014

The interaction between wheel and rail is the main source of noise in a tram that moving on the rolling track. Wheel and rail irregularities are the causes that initiate dynamic forces and vibrations. Noise is the result of vibrations generated due to defects located on the contact of these surfaces. Rolling noise levels reduction can be achieved by improving contact surface condition, mainly by wheel bogies reshaping
A Comparison of Composite Bars against Metallic Bars from the Mass per Unit Length Point of View
Authors: Miriţoiu Cosmin Mihai , Bolcu Dumitru , Stănescu Marius Marinel , Vîlcu Rosca , Ilincioiu Dan
Published: March 2014

There were built some new original composite sandwich bars with polypropylene honeycomb core and the exterior layers of the bars were made of epoxy resin reinforced with steel wire mesh. For these composite bars, there were determined the stiffness by using two different experimental methods: variant 1- using the Walter-Bai testing machine and variant 2- using the eigenfrequency of the first eigenmode. The errors between these two methods were determined. In the next stage of the paper, some metallic beams, equivalent from the stiffness point of view with the composite ones, were considered. Comparisons between them, from the mass per unit length point of view, were made.
Effect of Exploitation Conditions and Flaw Geometry on the Load Carrying Capacity of Casing Pipes for Oil Drilling Rigs
Authors: Rakin Marko , Medjo Bojan , Arsić Miodrag , Šarkoćević Živče , Sedmak Aleksandar
Published: March 2014

The subject of this work is examination of API J55 steel casing pipes manufactured by high frequency (HF) contact welding. Since the pipes were withdrawn after about 70 000 hours of service in an oil drilling rig, the influence of the exploitation conditions on the material properties is determined. Experimental analysis includes tensile, impact toughness and fatigue testing of the specimens cut from the exploited pipe and the new pipe manufactured from the same-grade material. Additionally, pipe with flaws (stress concentrators) is tested by subjecting to internal pressure. The analysed stress concentrators represent defects which are often found in the exploitation: localized corrosion damages (corrosion pits). They were simulated by machining on the external surface of the pipe wall. The behavior of the pipes with these defects is determined by strain measurement and finite element analysis in software package Abaqus. The dimensions of the defects are varied, in order to determine the dependence of load carrying capacity on their depth and length. Several expressions from the literature are applied for estimation of the maximum pressure in damaged pipelines, and the solutions are compared with the predictions of finite element models. Additionally, triaxiality values at the bottom of the defects are compared with those obtained on tensile specimens, having in mind the key role of this parameter in ductile fracture initiation.
Novel Testing Device for the Experimental Stress Concentration Analysis of Multilayer Textile Composites under In-Plane Compressive Load
Authors: Grüber Bernd , Hufenbach Werner , Gottwald Robert , Lepper Martin , Modler Niels , Zhou Bingquan
Published: March 2014

An analytically based calculation tool for the stress-strain analysis of multilayer composite plate structures with cut-outs is developed which offers high potential to be used in a sense as an analytical sub-model in combination with FE-Analysis Systems. For its validation extensive numerical and experimental investigations have to be carried out. Especially the examination of structures loaded by in-plane compression does not seem to be realizable by conventional testing techniques. That is why a novel testing device for the experimental stress concentration analysis of notched thin plate structures under in-plane compressive load is developed and its application in combination with an adapted optical measurement system is demonstrated.
Buckling Behaviour of the Delaminated Sandwich Plates under Combined Loads
Authors: Beznea Elena Felicia , Chirica Ionel
Published: March 2014

In the paper, a methodology to evaluate the influence of the central circular delamination on the buckling and postbuckling behaviour of the sandwich plates under shear and compression loading, used in ship hull structure, is presented. The parametric calculus was done for various values of loading ratios. The numerical tests on the delaminated plates are presented. Sandwich composite plates containing central delaminations are analyzed with respect to combined boundary shear and axial compression buckling. Finally, the graphical results for all values of loading ratio are presented.
Theoretical Meso-Model of Al2O3/ZrO2 Ceramic Response under Compression
Authors: Sadowski Tomasz , Marsavina Liviu
Published: March 2014

This paper presents theoretical modeling of two-phase ceramic composites subjected to compression. The meso-mechanical model allows for inclusion of all microdefects in the polycrystalline structure that exists at the grain boundary interfaces and inside the grains. The constitutive relations for the Al2O3/ZrO2 composite with the gradual degradation of the material properties due to different defects development were formulated.
Cracked Pre-Stressed Elastic Composite Subjected by Sliding Forces I. Mathematical Modelling
Authors: Craciun Eduard Marius , Nicolae Ionel , Rădoiu Viorel Bogdan , Carlig George , Mateescu Liviu
Published: March 2014

We consider one or two collinear cracks in a pre-stressed, orthotropic, linear elastic material representing a fiber reinforced elastic composite. Elastic incremental fields in the composite material, using Guzs representation theory, Cauchy-Riemann problem and critical values of incremental tangential stresses that producing crack propagation are obtained using Sihs generalized criterion.
Ultra-Large Unilamellar Nanosheets Efficiently Exfoliated from (Y0.95Eu0.05)2(OH)5NO3·nH2O and their Self-Assembly into Oriented Oxide Film with Enhanced Photoluminescence Properties
Authors: Zhu Qi , Li J.G. , Li Xiao Dong , Sun Xu Dong
Published: March 2014

Two dimensional nanophosphors of high quality play an important role in the miniaturization and intelligentization of opto-electronic components. In this present work, ultra-large (30μm) single crystals of (Y0.95Eu0.05)2(OH)5NO3·nH2O layered rare earth hydroxide (LRH) with a hexagonal shape have been synthisized via autoclaving the rare-earth nitrate/NH4OH reaction system in the presence of ammonium nitrate (NH4NO3). The nitrate ions, existing in the interlayer gallery of layered rare earth hydroxide, exhibit facile exchanges with oleate anions by hydrothermal anion exchange. Furthermore, the interlayer distance can thus be expanded from ~0.9 nm for the pristine LRHs to ~3.60 nm for the intercalated ones, which are then efficiently delaminated into unilamellar nanosheets with a lateral size of 10μm and a thickness of ~1.50 nm. The obtained nanosheets are single crystaline. Highly [11 oriented, dense (Y0.95Eu0.05)2O3 phosphor films with excellent optical transparency and a greatly enhanced luminescence intensity have been constructed via self-assembly of ultra-large unilamellar LRH nanosheets, followed by proper annealing.
Synthesis of (La0.95Eu0.05)2O3 Red Phosphors with Hydroxide Nanowires as the Precursor: Template-Free Hydrothermal Processing and Photoluminescent Properties
Authors: Wang Xue Jiao , Li Ji Guang , Zhu Qi , Sun Xu Dong
Published: March 2014

Ln (OH)3(Ln=La0.95Eu0.05) nanowires have been successfully synthesized through hydrothermal reaction, without using any template, from mixed solutions of the component nitrates. It was shown that neither solution pH (7.5-13) nor hydrothermal temperature (120 and 150 °C) significantly influences the phase structure and particle morphology of the product. The resultant Ln (OH)3nanowires are of uniform dimension and good dispersion. A homogeneous Ln2O3solid solution was yielded by calcining the hydroxide nanowires in the air at 800 oC. Under 285 nm excitation, the Ln2O3phosphor exhibits the characteristic red emission of Eu3+at ~630 nm and show emission behaviors clearly dependent on the calcination temperature, which were investigated in detail.
Composition, Structure and Electrical Resistivity of TiOx Thin Films Deposited by RF Magnetron Sputtering at Varied Substrate Temperatures
Authors: Su Hai Xia , Peng Zhi Jian , Fu Xiu Li
Published: March 2014

TiOx thin films were deposited by RF magnetron sputtering with TiOx (x<2) target at varied substrate temperatures. The composition and microstructure of the films was characterized by grazing incidence X-ray diffraction, scanning electron microscopy and Raman spectroscopy, which revealed that the films deposited at low temperatures were amorphous, and as the temperature increased up to 600 °C, the prepared films became crystalline and a TiO2 anatase phase was identified. Also the electrical resistivity of the as-prepared TiOx films was investigated as a function of the deposition temperature. The result indicates that with the raise of substrate temperature, the electrical resistivity of the deposited films decreased sharply.
Preparation of High-Performance Continuous Boron Nitride Fibers from Boracic Acid
Authors: Li Chuan Shan , Li Ru , Du Xiao Yong , Zhang Ming Xia , Tang Jie , Tang Jian Xin , Zhou Chang Ling , Wang Chong Hai
Published: March 2014

Continuous multi-filament boron nitride fibers have been prepared on a large scale using the melt drawn technique from a low-cost boracic acid. Boracic acid was heated to obtain the molten boric oxide in a melting tank. Molten boric oxide was melt spun in a conventional manner through an 200-tip bushing to produce a continuous multifilament yarn consisting of 200 filaments of boric oxide. Boric oxide fibers were nitrided in an ammonia and were annealed in an inert atmosphere while simultaneously subjecting the fibers to sufficient longitudinal tension as to at least prevent longitudinal shrinkage of the fibers. The resulting fibers, consisting essentially of boron nitride, were less than about 8 μm in diameter and greater than 500 m in length. It indicated that the boron nitride fibers has a sound mechanical function with tensile strength of 1.40 GPa. The continuous boron nitride fibers of high-performance were especially suitable for reinforcing plastic, ceramic or metal matrices in the preparation of fiber reinforced composites.
Novel Direct Coagulation Casting of Alumina Suspensions Using Y3+-Ion Releasing Substances as Coagulant
Authors: Dong Yue , Li Xiao Dong , Liu Shao Hong , Li Ji Guang , Sun Xu Dong
Published: March 2014

Direct coagulation casting (DCC) is a relatively new ceramic near-net-shape forming process which can form homogeneous ceramic green body with complex shape and high density. Direct coagulation casting of aqueous alumina slurries by adding Y3+ions, which have been frequently used as additive for the sintering of alumina ceramics, were studied. Two different kinds of Y3+-ion releasing substances, Y2O3powder and Y(NO3)3, were used as coagulants and were introduced into stabilized alumina suspensions directly after dispersing. Compared with that of Y2O3powder, both the coagulation time and the added amount required for a reasonable shaping were significantly reduced for using Y(NO3)3as coagulant. The effects of the two coagulants on the properties of the consolidated green bodies and sintered ceramics were studied. The mechanisms of coagulation induced by the addition of Y3+-ions were discussed on the basis of interactions between Y3+ions and the added polyelectrolyte dispersant.
Low-Temperature Sintering of SiC Reticulated Porous Ceramics Using Al2O3-SiO2 as Sintering Aids
Authors: Zhao Jing , Ru Hong Qiang , Wang Wei , Yue Xin Yan
Published: March 2014

Currently, one of the most popular methods for the production of reticulated porous ceramics (RPCs) is the polymer sponge method, which was invented by Schwartzwalder and Somers. SiC RPCs can be fabricated by using the A12O3-SiO2 as sintering aids at low temperature as 1200-1300 °C in cases with SiC (20-50 % (mass percent)). However, when the content of SiC powders (relative to total weight of solids) was higher than 50 % (mass percent), the most suitable sintering temperature was higher than 1400 °C. In this work, SiC reticulated porous ceramics (SiC RPCs) was fabricated via the polymer sponge method using Al2O3-SiO2 as sintering aids at 1100-1500 °C. In order to obtain SiC RPCs with optimized mechanical performance, the properties of the slurry and influence of sintering temperature have been investigated. It was found that, rheological properties, solid content of the slurry and sintering temperature all have influence on the physical and mechanical properties of SiC RPCs. In order to achieve optimal properties of SiC RPCs, the optimal pH value ,solid content, sintering temperature and content of silica fume were 11, 73.4 % (mass percent), 1300 °C and 17 % (mass percent), respectively.
Preparation of γ-AlON Transparent Ceramics by Pressureless Sintering
Authors: Chen Feng , Zhang Fang , Wang Jun , Tian Run , Zhang Jian , Sun Yi , Zhang Hai Long , Zhang Zhao , Wang Shi Wei
Published: March 2014

In this paper, AlON powders were prepared by carbothermal reduction and nitridation method. By adding a mixture of Y2O3, La2O3 and MgO as sintering agent, transparent AlON ceramics with high strength were fabricated by pressureless sintering at 1950°C for 8h under nitrogen atmosphere. The obtained ceramic had a relative density of 99.9% and average grain size of 150μm. The transmittance of the 2mm thick ceramics was 82.4% at 1100nm and flexural strength was 300 MPa.
Effect of Potassium Carbonate Addition on the Sintered Properties of Coal Fly Ash
Authors: Li Wen , Fan Bing Bing , Wang Bing Bing , Sun Bing , Zhang Liang , Pian Xiao Xuan , Chen Hao , Wang Chen Yang , Zhao Biao , Zhang Rui
Published: March 2014

In this project, coal fly ash was transformed into ceramic materials by adding a certain amount of fusing agent. Ash samples were compacted and sintered with the addition of potassium carbonate (K2CO3·1/2H2O) under a suitable sintering temperature range. Mineralogy and microstructure of the obtained products were characterized by means of X-ray diffraction and field emission scanning electronic microscope techniques respectively. The results indicate that K2CO3·1/2H2O facilitates the transformation of mullite and quartz phases above 800°C, and the mineralogy phases of the product is leucite (KAlSi2O6) and potassium aluminum silicate (KAlSiO4). In the process, K+interacts with oxygen atom and destroys the original lattice. The regular morphology of the sintered samples was confirmed by the observation under SEM, which reveals a uniform dense ceramic is formed at 900°C with the 40wt% addition of K2CO3·1/2H2O.
Study on the Variety of Rheological Properties and Thermal Analysis of Modified Coal Tar Pitch with 1,4-Benzenedimethanol
Authors: Shi Wu Chao , Dong Li Min , Li Qiang , Wang Chen , Liang Tong Xiang
Published: March 2014

Coal tar pitch (CTP) as carbon material was studied using 1,4-Benzenedimethanol (PXG) as modifier by p-toluene sulfonic acid (PTS) catalyst and the variety of rheological properties of modified coal tar pitch (MTP) was discussed. The apparent viscosity of CTP and MTP were measured using rotating coaxial-cylinder viscometer, and the relations between the apparent viscosity and temperature were studied. Thermal behaviors of CTP and MTP were analyzed with TG-DSC. The results showed that the viscosity of the MTP gradually decreased with the temperature rising and the viscous activation energy of the MTP is 72.92 kJ·mol-1, which was beneficial to the process for producing carbon materials and the carbon yield was greatly improved. Therefore, coal tar pitch modified with PXG was qualified to be an excellent carbon precursor.
Preparation of Industrial Watchcase of 5Y-Tetragonal ZrO2  by Microwave Sintering
Authors: Pian Xiao Xuan , Fan Bing Bing , Zhang Xin , Chen Hao , Wang Chen Yang , Zhao Biao , Zhang Rui
Published: March 2014

The industrial watchcases of 5Y-Tetragonal ZrO2were prepared by microwave sintering. Samples were sintered in a microwave chamber with TE666 resonant mode at 2.45GHz. The sintering temperature was from 1250°C to 1400°C. XRD and SEM techniques were used to characterize the samples. It is found that microwave sintering improved the phase change from t-ZrO2to m-ZrO2. Dense and homogeneous microstructure was obtained within the microwave-sintered samples and the average grain size was about 500nm. Compared to conventional sintering, microwave-sintered samples show higher density and hardness. And microwave-sintered samples were performed 130°C lower temperature. Optimized sample with the density of 6.1 g/cm3and Vickers Hardness of 16.2MPa is microwave-sintered at 1350°C for 30min.
Homogeneous Microstructure of ZrO2-BN Composites with In Situ Synthesized BN
Authors: Chen Lei , Wang Yu Jin , Hammadi Kamal , Zhou Yu
Published: March 2014

A new process was used to improve microstructure homogeneity of ZrO2-BN composites. Boric acid was deposited on the surface of ZrO2 particles by heterogeneous precipitation method from aqueous solution of boron oxide under the action of heat by evaporation. In order to improve the microstructure homogeneity, the mixture powder was stirred over-vigorously until transforming into the highly viscosity slurry. Subsequently, the obtained mixture powders were dried, nitrided at 900 °C in ammonia and crystallized at 1500 °C in nitrogen atmosphere to obtain in-situ synthesized BN coated on the surface of ZrO2 composite particles. Finally, ZrO2-BN composites incorporated with 30 vol. % BN were prepared by hot-pressing. The SEM microstructure and fracture surface of ZrO2-BN composites revealed that in-situ synthesis BN particles were dispersed in the ZrO2 matrix homogeneously.
Preparation and Thermal Cycling Resistance of SiBCN(O) Coating
Authors: Feng Ze Long , Guo Zhi Min , Lu Biao , Zhang Yue
Published: March 2014

An oxidation protective coating of SiBCN(O) is prepared by slurry method, using polyborosilazane (PBSZ)-ethanol solution as the precursor. The dense and uniform coatings are obtained by pyrolysis and sintering at 1573K. The sintering temperature is significantly reduced and the densification is improved by introducing oxygen. The coating shows high oxidation protecting performance during the thermal shock between 1773K and room temperature for 10 cycles. The oxidation mechanism of the coating is studied and the results show that two stages are included: the relatively stable stage and the weight loss stage.
Preparation and Characterization of SiC Coating on Graphite Substrate
Authors: Huo Yan Li , Chen Shu Guang , Liang Hai Long , Wang Chun Peng , Zhou Jian , Hu Chuan Qi , Liu Hai Lin , Wang Guang Hai
Published: March 2014

High thermal conductivity and dense SiC coating were fabricated by chemical vapor deposition (CVD) on surface of different graphite at temperature of 1100°C. The results indicated that the thickness of the coating influences the quality of coating. There was no crack in coating when thickness of the coating is less than 0.3mm. The structure of graphite affected the reaction badly. When the graphite is coarse and porous the reaction is chemical vapor infiltration (CVI) and the interface of coating and substrate isnt obvious. When the graphite is dense and smooth, the coating is covered in surface of graphite, the interface is found between the coating and substrate. Optical microscope and SEM were used to observe the surface and cross-section morphology and microstructure of coatings. It shown coating and substrate had a good combination and the deposited grains mainly showed equiaxed form with the crystallite size of 30 nm at 1100°C.
In Situ Preparation and Mechanical Properties of (ZrB2+ZrC)/Zr3[Al(Si)]4C6 Composites
Authors: Yu Lei , Yang Jian , Qiu Tai
Published: March 2014

Fully dense (ZrB2+ZrC)/Zr3[Al (Si)]4C6 composites with ZrB2 content varying from 0 to 15 vol.% and fixed ZrC content of 10 vol.% were successfully prepared by in situ hot-pressing in Ar atmosphere using ZrH2, Al, Si, C and B4C as raw materials. With the increase of ZrB2 content, both the bending strength and fracture toughness of the composites increase and then decrease. The synergistic action of ZrB2 and ZrC as reinforcements shows significant strengthening and toughing effect to the Zr3[Al (Si)]4C6 matrix. The composite with 10 vol.% ZrB2 shows the optimal mechanical properties: 516 MPa for bending strength and 6.52 MPa·m1/2 for fracture toughness. With the increase of ZrB2 content, the Vickers hardness of the composites shows a near-linear increase from 15.3 GPa to 16.7 GPa. The strengthening and toughening effect can be ascribed to the unique mechanical properties of ZrB2 and ZrC reinforcements, the differences in coefficient of thermal expansion and modulus between them and Zr3[Al (Si)]4C6 matrix, fine grain strengthening and uniform microstructure derived by the in situ synthesis reaction.
Influence of Coated Composite Powders on the Properties of ZrB2-YAG-Al2O3 Ceramics
Authors: Song Jie Guang , Wang Xiu Qin , Wang Fang , Li Shi Bin , Ji Gang Chang
Published: March 2014

ZrB2, YAG and Al2O3 are widely applied because of some excellent performances, but ZrB2 is easily oxidized in the high-temperature air. To make the ZrB2 ceramics obtain better oxidation resistance, high-density ZrB2-YAG-Al2O3 ceramics were prepared. The influences of coated composite powders on the densification and the oxidation resistance of ZrB2-YAG-Al2O3 ceramics were investigated. The 80wt%ZrB2-YAG-Al2O3 multiphase ceramic materials from different composite raw materials with the spark plasma sintering technique were successfully prepared. The densification of ZrB2-YAG-Al2O3 ceramics with Al2O3-Y2O3 composite powder coated is easier than that of ZrB2-YAG-Al2O3 ceramics with YAG-Al2O3 powder mixed. The reaction temperature is lower than the 1100¡æ for synthesizing YAG powders from Al2O3-Y2O3 composite powders. The weight gain are increased with increased the oxidation temperature. B2O3 is reacted with Al2O3 to form Al18B4O33, Al18B4O33 is melted and coated on the surface of ceramics to form a protective layer for the oxidation resistance of ceramics at high temperature. The oxidation weight gain of ZrB2-YAG-Al2O3 ceramic with Al2O3-Y2O3 composite powder coated is lower than that of ZrB2-YAG-Al2O3 ceramic with YAG-Al2O3 powder mixed.
Preparation and Properties of Cu Matrix Reinforced with Ti2AlN Ceramic Particles
Authors: Zhang Dan Dan , Zhan Zai Ji , Guo Chang Hong , Tang Gong Min
Published: March 2014

Cu matrix composites with various contents of Ti2AlN were fabricated by powder metallurgy using spark plasma sintering (SPS) method. Ti2AlN ceramic particles were pre-treated by electroless copper plating, the result showed that Ti2AlN reinforcement and Cu matrix were strongly bonded. The effects of Ti2AlN content on microstructure, electrical resistivity and mechanical properties were systematically investigated. With the addition of low fraction of Ti2AlN, the hardness and tensile strength of matrix were improved without losing the fracture toughness too much. Tensile strength of Ti2AlN/Cu composites were about 380 MPa with the content of 7 wt. % reinforcing phase, and the conductivity of the composites remained about 61.5 % IACS. Moreover, the wear tests illustrated that the loads were effectively born by the Ti2AlN reinforcement, the main tribological mechanism changed from adhesive wear to abrasive wear compared with Cu, thus the friction and wear resistance was also obviously improved.
AlN/CNT Composites Ceramics by Spark Plasma Sintering
Authors: Liang Hai Long , Wang Chun Peng , Huo Yan Li , Hu Chuan Qi , Huang Xiao Ting , Tang Jie
Published: March 2014

Highly dense AlN/CNT composite ceramics with 1-10% volume fractions of CNT were fabricated by spark plasma sintered (SPS) at 1400°C-1700°C. The results indicated that origination diameter of AlN had a great effect on microstructure and thermal conductivity. In details, for the system with AlN origination diameter of nanosized, the tubular structure of CNT has not been destructed, but when micro-sized AlN powder was adopted, the structure of CNT showed unstable at high temperature. Even though the degradation with incorporation of CNT into AlN, thermal conductivity of sintered AlN/CNT composites ceramics was evidently improved by adjusting content of additive Y2O3and the sintering process. Both the real part and imaginary part of the composites of Ka-Band (26.540.0 GHz) increase with the increase of CNT content, in which the increase of imaginary part is more than that of real part, resulting in an increase of loss factor. The AlN/ CNT thermal conductivity composites with appropriate CNT content and sintering temperature possess good dielectric dissipation and thermal conductivity.
Effect of Amorphous Phase on Mechanical Properties of SiC/Cu Composites
Authors: Sun Bing , Fan Bing Bing , Wang Chen Yang , Wang Bin Bin , Li Wen , Li Xin Fang , Chen Hao , Pian Xiao Xuan , Zhao Biao , Zhang Rui
Published: March 2014

In this study, glassy phase is formed by SiO2-K2O addition to serve as amorphous grain boundary transition layer. SiC (SiO2-K2O) / Cu composite material were prepared by two-step coating method and hot pressing sintered below 770°C, 30MPa for 1.5h, using α-SiC as main reinforced phase, SiO2-K2O as grain boundary and Cu as matrix. The Cu-SiC volume ratio was 75:25. The SiO2contents were 5vol.%, 10vol.%, 15vol.%, 20vol.% and 25vol.% of the total volume of the SiC / Cu. XRD and SEM techniques were used to characterize the composite particles and the sintered compacts; Archimedes method, Vickers hardness tester, universal testing machine to test the apparent porosity of the composite materials, the Vickers hardness and the bending strength, respectively. The results showed that with increasing of glassy phase contents, the Vickers hardness and the bending strength first rise and then drop, at the same time, it shows the opposite tendency for the apparent porosity. The sintering samples with the SiO2content of 15vol.% have the optimum mechanical properties, the Vickers hardness reached 1.49 GPa, and the bending strength was close to 235 MPa.
A Comparison of the Application between Different Proportional nHA / PLA in Alveolar Bone Preservation
Authors: Bai Yang , Liu Na , Chen Jian Feng , Zhao Li Sheng , Deng Bin , Wen Ning , Liu Hong Chen
Published: March 2014

Objective: To compare the effectiveness of different proportional nHA / PLA application in alveolar bone preservation. Methods: After extraction, apply extraction socket filling based on the alveolar bone defect model due to absorption in Beagle dog. Implant materials are divided into 3 different groups: nHA / PLAI, nHA / PLAII and the control group. Samples of the alveolar bone were collected at Week 4 and 8, respectively for the bone resorption assessment, bone density measurement, and histological examination. Results: After nHA / PLA implantation, the alveolar bone preservation was significantly improved. There was no difference in the alveolar bone preservation between the nHA / PLAI and nHA / PLAII groups. However, the sample which are 8w from group I, have higher bone density and have complete absorption in their dental material nest .Therefore group I is better than group II. Conclusions: The results can provide a reliable basis for the application of alveolar bone preservation in basic research and selection of clinical materials.
In Situ Formation of Mullite-Al2O3 Refractory Ceramic from Al-Matrix Mixtures
Authors: Gu Xing Yong , Li Ping , Dong Wei Xia , Luo Ting
Published: March 2014

Two types of mullite-Al2O3 composites were designed and sintered in situ from different composition containing Al composites e.g. kaolin, alumina hydroxide and calcined bauxite etc, and auxiliary additives. The phase composition and microstructure were studied using X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. Bulk density, apparent porosity, thermal expansion coefficient and bending strength were also measured. The two samples exhibited XRD reflections characteristic of alumina and mullite phases. The amount of these phases depended on starting batch compositions, and reaction of starting and auxiliary materials together to form mullite. Because of in-situ formation of mullite fiber, the bulk density and bending strength were improved and apparent porosity was decreased for the composites with uniform microstructure. The presence of high mullite phase was found to decrease the thermal expansion coefficient. The potential effect of these morphologies and phase on properties was discussed. These mullite-Al2O3 composite was expected to have major applications in the areas of refractory material.