Strength Of Ceramic Materials Research Articles

The usage of water conditioning sludge from heat power industry enterprises in wall ceramics production

The paper considers the ecological problems of water conditioning systems at heat power industry facilities. It is noted that the stable operation of water-heating equipment is provided with the quality of feed water. Various water-soluble salts, which can incrust the inner walls of boilers or pipelines, are removed from the natural water. For desalination of natural water the physical-chemical methods are mostly used. The by-product of desalination or chemical water-conditioning systems is the sludge waste. This work presents the results of using chemical water conditioning sludge from JSC Verofarm in the raw charge for wall ceramics production. The sludge is a finely-divided powder, the mineral composition of which is presented with calcium and magnesium carbonates, brucite and iron compounds, which make the sludge pink. It has been determined that the baking of sludge-containing ceramic samples at temperature 1000°C results in dissociation of calcium and magnesium carbonates with the formation of gaseous products H2O and CO2, which make the structure of ceramic materials porous. The presence of iron compounds in the raw charge promotes the formation of low-temperature silicate melt, which intensifies the baking process of ceramic samples. The optimal sludge content in the charge that doesn’t reduce the strength characteristics of wall ceramics is 10%. Such sludge content forms the liquid phase on the surface of the raw mix’s particles, which solidifies the forming pores. The increase of sludge content up to 20% intensifies gas generation; the amount of the formed liquid phase is not sufficient, which increases porosity and reduces the density and strength of ceramic materials. At that, the engobe layer is formed on the surface of the obtained wall ceramics samples. The wall ceramics products, obtained with the use of chemical water conditioning sludge, can be used as structural heat-insulation materials in making building envelopes or interior partitions.

Residual Lifetime Determination of Low Temperature Co-Fired Ceramics

The effect of subcritical crack growth is nowadays intensively studied mainly in relation to the strength of ceramic materials. The main aim of the contribution is to describe behavior of micro-crack propagating in the Low Temperature Co-fired Ceramics (LTCC) under subcritical crack growth (SCCG) conditions. The micro-crack behavior is significantly influenced by residual stresses developed in the LTCC due to different coefficients of thermal expansion of individual components. Two-dimensional numerical model was developed to simulate micro-crack propagation through the composite. The micro-crack propagation direction was determined using Sih’s criterion based on the strain energy density factor and the micro-crack path was obtained. The residual lifetime of the specific ceramic particulate composite (LTCC) was estimated on the basis of experimental data. The paper contributes to a better understanding of micro-crack propagation in particulate ceramic composites in the field of residual stresses.

Failure Analysis of Ceramic Substrates Used in High Power IGBT Modules

High voltage power modules are used in numerous applications to build high power converters. Technically, these modules are made of different materials and among them, dielectric materials are organic and inorganic. Organic insulators (gels) are used to avoid corona discharges in the vicinity of connecting wires and high voltage dies (diodes and transistors) and to protect them from moisture and contaminants. Inorganic insulators (ceramic substrates) are used to insulate the high voltage which dies from the grounded elements and to transfer heat to the heat sink. Despite being used since the late 90s, there is a lack of fundamental knowledge about the electrical properties of these substrates. Consequently, manufacturers tend to assure the reliability by over sizing them. As there are no clear rules for how to do that, failures occur, leading to the converter shutdown. The aim of this study is to bring new information about the understanding of the dielectric strength of ceramic materials used in these modules. We have focused our work on the correlation between the mechanical and the dielectric properties of ceramics by using relevant experiments. We provide new information about the impact of existing cracks on the ceramic dielectric failure, according to the electromechanical breakdown model. Our conclusions bring crucial information about the precautions to be taken during manufacturing and implementation of these substrates in power modules to reduce the likelihood of the particular causes of failure.

Error Analysis of Ceramic Materials Fracture Toughness Measured by the Single Edge Notched Beam Method

In this study, the fracture toughness of ceramic materials such as Al2O3, SiC, Si3N4, ZrO2 were measured by the SENB method and IF method respectively. The results shown that the value of fracture toughness obtained from the SENB method is significantly higher than the IF method. When the notch width is fixed, with the flexural strength of ceramic materials increasing, the error of fracture toughness from the SENB method compared to the IF method is increased. For example, the flexural strength of ZrO2 is about 847MPa and the error of fracture toughness from the SENB method compared to the IF method is 50.14%, the flexural strength of Al2O3 is about 338MPa and the error of fracture toughness from the SENB method compared to the IF method is only 4.52%.

Fractography of biaxial tested Si3N4-specimens

Abstract The strength of ceramic materials is limited by flaws which are distributed in the volume or on the surface of the material. Commonly, fractographic investigations are performed after the strength tests to interpret the strength values. The relatively new Ball-on-Three Balls (B3B)-bending test applies a biaxial stress state (which is more searching for cracks than a uniaxial stress state) on the specimen. To identify typical fracture initiating flaws and to get a better understanding of the fracture behaviour of B3B-specimens a systematic fractographic investigation was performed on 260 silicon nitride specimens divided into batches with different surface qualities. It could be shown that in most cases (at least those in which origins could be clearly identified) surface or near surface located defects were responsible for failure. On specimens with poor surface qualities, surface defects were introduced through machining. On specimens with a better surface quality, volume defects, which were exposed on the surface by polishing, could be identified as fracture origins. In only a few cases defects in the bulk were fracture origins.

Effect of residual stresses on the strength of ceramic materials (Review)

The causes and laws of the appearance of residual stresses in ceramic materials during technological operations (sintering, annealing, neutron irradiation deformation processing, chemical interaction with a medium) are analyzed using our results and the data obtained by other researchers. The effect of residual stresses on the strength during mechanical static and cyclic loading, the thermal resistance, and the cracking resistance is considered.

Contact Strength and Cracking of Laminar Ceramics

AbstractThe paper deals with the determination of strength of laminar ceramics by mechanical tests in bending and contact modes. The bending and contact modes are simulated by the four-point bending test, and by single-cycle contact test using rollers or spheres, respectively. In general, the determination of strength of ceramic materials results from statistical methods which are usually represented by the Weibull analysis. The Weibull analysis comprises the determination of the characteristic strength

Probabilistic Thermal-Shock Strength Testing Using Infrared Imaging

A thermal-shock strength-testing technique has been developed that uses a high-resolution, high-temperature infrared camera to capture a specimen's surface temperature distribution at fracture. Aluminum nitride (AlN) substrates are thermally shocked to fracture to demonstrate the technique. The surface temperature distribution for each test and AlN's thermal expansion are used as input in a finite-element model to determine the thermal-shock strength for each specimen. An uncensored thermal-shock strength Weibull distribution is then determined. The test and analysis algorithm show promise as a means to characterize thermal shock strength of ceramic materials.

Strength of free-standing chemically vapour-deposited diamond measured by a range of techniques

The strength of free-standing chemically vapour-deposited diamond was determined using a bursting-disc test, a three-point bend test and a four-point bend test. The bursting-disc technique has advantages for determining the strength of ceramic materials since the maximum tensile stress is at the centre of the disc. The much smaller stresses near the sample edges are rarely responsible for failure and so edge effects are negligible. However, the bursting-disc test is often impractical for ascertaining the strength of chemically vapour-deposited diamond since the cost of samples is high. A three-point bend test is often employed instead, since it may be performed on smaller samples. However, the area stressed in the three-point bend test is smaller, and so there is less chance of stressing a large flaw, resulting in higher strength values. A further disadvantage is that specimen edges are stressed and, unless the specimen sides are polished, as well as its faces, misleading results may be obtained (although this is not the case for chemically vapour-deposited diamond). A four-point bend test is often used because it stresses a larger volume of material than the three-point bend test and so the results are more reliable. Furthermore, the diamond used in a four-point bend test can be of similar size to those used in a three-point bend test and so the expenditure is comparable. However, ensuring that the four-point bend test is applied correctly is technically more difficult. Strength data are reported for both the growth and the nucleation sides, for difference nucleation densities and for as-received and polished samples.

Investigation of properties of electric arc ion deposited TiN coating on Al2O3-based ceramic composite

Electric arc ion deposition technique was adopted to deposit TiN coating on Al2O3-based ceramic composite. Scanning electron microscopy and secondary ion mass spectrometry were used to analyze the microstructure, phase constitution, and quality of the TiN coating and the interface. Surface roughness and micro-hardness of the TiN coating were measured to evaluate its quality. Flexural strength of ceramic materials is dependent on both their inherent resistance to fracture and the presence of defects, thus it was used to investigate the effect of electric arc ion deposition technique on the surface modification of Al2O3-based ceramic composite. Experimental results show that the higher the deposition bias voltage, the better the coating quality. The TiN coating is homogeneous, with a uniform surface, and free of defects when the deposition bias voltage is 300 V. The TiN coating strongly adheres to the Al2O3-based ceramic composite, and the observed elemental interface diffusion strengthens the interface bonding.

Use of Waste Materials from the Production of Synthetic Rubber for Preparing Aluminosilicate Ceramics

An aluminum-silicon-chromium powder (ASC) extracted from waste gases in synthetic rubber production is used as an addition to kaolin-based ceramics, and its effect on the kinetics of sintering, compressive strength, and phase composition of mullite-corundum and corundum ceramic materials is studied. The strength of ceramic materials is mainly determined by the amount and composition of the mullite component. The effect of mechanochemical activation in an aqueous medium on the physicochemical properties of the mullite-corundum materials is studied.

Elimination of low-quality ceramic posts by proof testing

Objectives. Prosthetic posts made of zirconia ceramics are beneficial because of their esthetic advantages. The mechanical reliability of ceramic posts is limited because of the strength level and the large scatter in strength of ceramic materials. The hypothesis of this study is that the failure of ceramic posts in vivo, which occur on low-quality posts because of critical microscopic defects can be excluded using the so-called proof test technology. Methods. The theory of the proof test technology is explained in detail in this study. In the experimental part 22 ceramic posts were tested at different proof load levels using a stepwise rotating four-point bending proof test device. Results. The experimental failures deviated from the theoretical failure probabilities by 0.24–12.69%. The deviation would be further reduced in a serial proof test using batches with a greater quantity of posts. The test eliminated those posts, which contained microscopic defects above a critical size of clinical relevance. Significance. The technology can help to reduce clinical failures of non-vital abutment teeth with ceramic posts, which are caused by critical microscopic defects of the ceramic material as a result of the industrial manufacturing process.

On Targets Strength of Ceramic Materials for Impacting Penetration

On Targets Strength of Ceramic Materials for Impacting Penetration

Measurement of Strength of Ceramic Materials Using a Miniaturized Bending Method

Measurement of Strength of Ceramic Materials Using a Miniaturized Bending Method

Penetrable ceramic materials based on clays with a controllable porous structure

The effect of isometric and fiber organic and inorganic additives such as chamotte, carbon black, hydrophilic graphite, glass fiber, mullite-siliceous fiber, carboxymethyl cellulose, and cellulose introduced jointly and separately on the penetrability, maximum pore size, size distribution of penetrable pores, and mechanical strength of ceramic materials based on low-melting clay is investigated. It is shown that the pore structure can be controlled by simultaneous introduction of additives of different natures. The materials obtained have a maximum pore size of 1.2–2.9 µm, a gas penetrability of 0.150 µm2, and satisfactory mechanical strength. The materials can be used as ceramic filters.

Influence of reactor radiation on α-Al2O3 in electrically insulating ceramic

Under the action of radiation, structural changes occur in ceramic materials; these changes influence its mechanical properties and corrosion resistance. Neutron resistance has the strongest effect, inducing a number of complex processes. Most ceramic materials consist of one or more crystalline phases cemented by glass phases. Neutron radiation produces opposite density changes in the crystalline and glass phase. The conflict between these processes in the ceramic leads to increase in radiation resistance, which is the essence of the compensation effect. Thus, on irradiation, the density of crystalline quartz in the free state decreases by 15%, while the density of quartz glass increase by 3%, with corresponding changes in the volume of the phases. In porcelain, such changes facilitate an increase in strength. The radiational strength of ceramic materials was investigated - in particular, the structural changes in the irradiation of the ceramic by fast neutrons in a flux of no more than 2{center_dot}10{sup 20} cm{sup -2}. The main effects noticed after irradiation of the ceramic by fast distance and decrease in intensity of the diffractional maxima in the crystalline phases of the ceramic, for example, in the {alpha}-Al{sub 2}O{sub 3} phase of the ceramics microlite, GB-7, ultraporcelain, and 22KhS. Inmore » the initial state, GB-7 ceramic has a homogeneous, analogous, but the {alpha}-Al{sub 2}O{sub 3} crystals are smaller. According to chemical analysis, the mass fraction of aluminum oxide in GB-7 and 22KhS is 97.09% and 95.14%, respectively.« less

Influence of production factors on the strength of ceramic materials

1. It is experimentally shown that the 95% aluminum oxide-base ceramic has the highest compressive strength among the materials considered, σc=3100 MPa, which is almost 15 and 30% more than the similar characteristics for cast STL-10 pyroceram and 13v technical glass, respectively. 2. The difference between the axial compressive, tensile, and pure bend strengths of specimens cut from sections and parts of chemically resistant porcelain and ceramic VIII produced by forming of a plastic mixture and slip casting in gypsum molds is from 25 to 40%. At the same time the difference between the compressive strength of specimens of ceramic VIII oriented at a right angle in cutting from the nozzle type part produced by slip casting in a gypsum mold reached 60%. 3. The axial compressive strength of the investigated ceramics increases with an increase in aluminum oxide content and decreases with an increase in silicon dioxide content. The bend strength of the ceramics may be increased by 15–80% by selection of the optimum machining conditions and firing temperature of the sections and by decreasing the porosity of the material. 4. The spread in experimental values of the strength of aluminum oxide-base ceramic materials under bending conditions, conditionally characterized by the sample variation coefficient, may be decreased to 8–12% by decreasing the porosity of the material and also by selection of the optimum machining conditions.

Reducing the consumption of zircon concentrate during the synthesis of glazes for tiles

i. V, E. Vainberg and A. G. Kozlova, "Acoustic method for controlling the strength of ceramic materials," Steklo Keram., No. i0, 19-21 (1986). 2. K. K. Strelov and I. D. Kashcheev, Technological Control of Refractories Production [in Russian], Metallurgiya, Moscow (1986). 3. V. V. Trofimov and V. I. Beloturov, "Effect of firing on the strength of ceramic systems," in: Mechanisms of Damage and the Strength of Heterogeneous Materials [in Russian], Leningrad (1985), pp. 202-205. 4. A. V. Lykov, Theory of Thermal Conductivity [in Russian], Vysshaya Shkola, Moscow (1967). 5. Handbook of Thermal Engineering [in Russian], Energiya, Moscow (1976), 6. Heat and Mass Transfer. Thermal Engineering Experiments: A Handbook [in Russian], Energoizdat, Moscow (1982).

The influence of subcortical crack growth on the strength of ceramics

Analytical and numerical solutions of subcritical crack growth equations are presented in order to examine the effects of loading rate, environment and structural parameters on the strength of ceramic materials. It is demonstrated that with the usual testing conditions the strength is almost independent of the macroscopic fracture toughness K c. Instead, a subcritical stress intensity factor K ∗ determines the macroscopic fracture behaviour. This K ∗ can be estimated from strength measurements under inert and corrosive conditions. Experimental results on Al 2O 3 ceramics reveal K ∗ to depend on grain boundary strength.

Strength of ceramic materials containing small flaws

Ceramic strength values for different flaw sizes, grain sizes and notch radii are analyzed with a grain-fracture model. The critical stress-intensity factor for small flaws is lower than that for large cracks. Therefore, conventional LEFM is not applicable for estimating ceramic component strength. However, the relationships between the ratio of equivalent crack length and mean grain diameter, a e d ,and the ratio of critical stress-intensity factors for short and long cracks, K c K Ic ,are almost identical for various kinds of ceramic materials. This fact is well expressed by the model. Moreover, both the effect of grain diameter on plain specimen strength and that of notch-root radius on the notch-toughness value are explained well with the model utilizing the K Ic value of materials.