The Limitation of Evaluating Thermal Shock Resistance of Al2O3-SiO2 Refractory by Measuring Strength Loss Rate

2011 ◽  
Vol 295-297 ◽  
pp. 2309-2313
Author(s):  
Xin Liu ◽  
Dian Li Qu ◽  
Zhi Jian Li

This paper deeply studied the limitation of evaluating the thermal shock resistance of Al2O3-SiO2 refractory by measuring Strength Loss Rate (SLR). By means of supersonic, X-ray diffraction (XRD), the results were drawn as followed.1)After the thermal shock experiment for mullite based A-S refractory, which were composed by mullite and corundum, the supersonic velocity slowed down as it going through the sample while the cold crushing strength abnormally increased at initial state.2) The strength increased remarkably with the ascending of mullite fraction.3)It is inadequate to evaluate the thermal shock resistance of mullite based A-S refractory by strength loss rate.

2013 ◽  
Vol 634-638 ◽  
pp. 2358-2361
Author(s):  
Jun Cong Wei ◽  
Li Rong Yang

The effects of Si3N4 addition on the room temperature physical properties and thermal shock resistance properties of corundum based refractory castables were investigated using brown corundum, white corundum and alumina micropowder as the starting materials and pure calcium aluminate as a binder. The phase composition, microstructure, mechanical properties of corundum based castables were investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that as the increase in Si3N4 addition, the bulk density decreased and apparent porosity increased, the cold strength deduced. However, the residual strength rate increased. That is, the thermal shock resistance was improved. This is because even though the introduction of Si3N4 inhibited the sintering of material and deduced the compactness, microcracks were produced in the materials due to a difference in thermal expansion coefficient. So the thermal shock resistance of corundum based castable was improved.


2020 ◽  
Vol 14 (1) ◽  
pp. 6514-6525 ◽  
Author(s):  
Mohammed A. Almomani ◽  
Mohamad I. Al-Widyan ◽  
Sulaiman M. Mohaidat

The high strength-to- weight ratio of titanium alloys allows their use in jet engines. However, their use is restricted by susceptibility to oxidation at high temperatures. In this study, the possibility of increasing the operating temperature of titanium alloys through using Yttrium Aluminum Oxide (YAG) as a thermal barrier coating material for Ti-6Al-4V substrate is studied. The study concludes that YAG can be utilized to increase the operating temperature of Ti-6Al-4V titanium alloy from around 350 °C to 800 °C due to its low thermal conductivity and phase stability up to its melting point. In addition, its lower oxygen diffusivity in comparison with the standard YSZ material will provide a better protection of the titanium substrate from oxidation. In this work, coating was created using atmospheric plasma spray. X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) were used to examine coatings' composition and structure. The coating was characterized by thermal shock test, Vickers hardness test and adhesion strength test. X-ray diffraction indicated that the coating was of a partially crystalline Y3Al5O12 composition. The coating was porous with excellent thermal shock resistance at 800 oC, with a Vickers micro-hardness of 331.35 HV and adhesion strength of 17.6 MPa.


Author(s):  
V. V. Primachenko ◽  
I. G. Shulik ◽  
I. V. Khonchik ◽  
T. G. Tishina

Effect investigation of an addition amount of spherical alumina on the properties of ramming mullite-corundum mixes of the MMK-90 (on a binder of an aqueous solution of orthophosphoric acid) and MMKPBF (with a MgO addition on a borophosphate binder) brands, as well as samples from them, have been carried out. As a result of the carried out studies, it was found that the use of an optimal amount (4 %) of spherical alumina in the composition of ramming mullite-corundum mixes provides an increase in by 30 % in the cold crushing strength of samples made from them, fired at a temperature of 1580 °C, while maintaining at sufficiently high level indicators of their thermal shock resistance and slag resistance. The indicated alumina use in the composition of the MMK-90 mix during high-temperature firing of samples leads to an intensification of the mullite synthesis process. In fired samples from the MMKPBF mix, the spherical alumina forms a dense intergrowth of "felt-like" structure, which reinforces the structure, increasing the strength and thermal shock resistance of the samples. Indicators of physical and chemical properties of ramming mullite-corundum mixes of improved composition and samples made from them (for MMK-90 and MMKPBF mixes, respectively): chemical composition, wt. %: Al2O3 — not less than 90.0 and 85.0; SiO2 — within 3.2-5.0 and no more than 2.5; Fe2O3 — no more than 1.0 and 0.6; P2O5 — in the range of 2.5-3.5 and 0.5-1.0; grain size composition, mm — 3-0; cold crushing strength after firing at a temperature of 1580 °С — 110 and 70 N/mm2; thermal shock resistance — > 20 thermal cycles 950 °С — water. Ramming mullite-corundum mixes of improved composition are recommended for use in various heating units with high specific mechanical loads on the lining.


2020 ◽  
Vol 94 (2) ◽  
pp. 414-453
Author(s):  
Małgorzata Daszkiewicz ◽  
Piotr Łuczkiewicz ◽  
Jörg Kleemann ◽  
Aneta Kuzioła

AbstractThe necropolis at Malbork-Wielbark was excavated from 1927 to 1936 and 2008 to 2019. This burial ground is the eponymous site of the Wielbark culture. To date, over 2000 burials, both inhumation and cremation (pit and urn graves), have been recorded at this site, attesting to its continuous use from the Early Pre-Roman Iron Age (phase A1) to the early Migration Period (phase D1), with particular emphasis on the Roman Period. The cemetery site partially overlies and damages an earlier Iron Age settlement of the Pomeranian culture.Laboratory analyses were carried out on 113 pottery sherds. The series of samples chosen for analysis reflected, as far as was possible, all relative chronological phases and vessel shapes. The pottery was analysed using a step by step strategy built on the results of MGR-analysis (i. e. the classification of samples based on their matrix type) and on a macroscopic assessment of clastic material. In addition, an estimation of chemical composition by portable energy-dispersive X-ray fluorescence (pXRF) was available for each sample. After they had been classified, samples were selected for chemical analysis by wavelength-dispersive X-ray fluorescence (WD-XRF), estimation of physical ceramic properties (open porosity, water absorption and apparent density), Kilb-Hennike analysis (K-H analysis), thin-section studies using a polarising microscope, a study of surface phenomena by RTI (Reflectance Transformation Imaging), thermal analysis (TG-DTG-DTA), X-ray diffraction analysis and functional properties analysis (water permeability and thermal shock resistance), as well as experimental estimation of magnetic properties.The results of MGR-analysis carried out on ceramic samples taken from 113 potsherds revealed that all of the pottery was made from various non-calcareous clays with fine-grained iron compounds homogeneously distributed in the matrix. It was decided not to carry on determining/using MGR-groups, as nearly every sherd represents a different MGR-group. This means that these vessels were made during different production cycles. The differences in thermal behaviour between samples were attributed only to matrix-type groups. It can be concluded that 85 % of the total sherds were made from plastic raw materials of the same provenance, and that the same matrix-type groups occurred in all chronological phases. The percentage of vessels made of particular raw materials indicates a significant difference in the preferences of Pomeranian Culture potters and those of Pre-Roman Iron Age, Early Roman Period and those of the Late Roman Period, when one type of raw material disappears from use. This last period is also characterized by an increase in the number of vessels fired in a reducing atmosphere. Standardization is also evident in vessel-wall thickness, which falls within a narrow range of values, on the other hand combined with a large variety in grain sizes up to very large ones and with a wide range of open porosity values, which in turn points to a lack of care in the preparation of the ceramic body. Vessels that may have been non-local origin are noted in all chronological phases. Analysis of functional properties (water permeability and thermal shock resistance) revealed that the pottery deposited in graves included fully functional wares, such as cooking pots, as well as vessels intended solely as grave goods.More than a few samples evidence the use of a slow-rotating potter’s wheel, and it is also possible that a template was used for forming vessel rims. However, there are very few examples of truly technologically advanced vessels. The technology is generally tailored to the desired type or form of vessel.


2016 ◽  
Vol 852 ◽  
pp. 1000-1005 ◽  
Author(s):  
Dong Xing Fu ◽  
Jing Na Liu ◽  
Er Bao Liu ◽  
Zhao Bin Cai ◽  
Xiu Fang Cui ◽  
...  

The interface properties of multi-layered functionally graded Cr3C2-NiCr coatings deposited by plasma spraying technique were experimentally studied in this paper. The microstructure and phase structure of coatings were studied with scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The thermal shock resistance was investigated by cyclic heating and cooling tests using an electro-calefaction furnace. The crack appearances of the coatings were observed carefully. Results show that the plasma sprayed multi-layered functionally graded coatings are compact and the adhesion between the layers and the substrate is good. The coatings have better macro-hardness than the substrate, and the 6-layers coating has the highest macro-hardness and the best wear resistance. Besides, the micro-hardness of coatings increases with increasing content of Cr2C3 in coating materials. Results of cyclic thermal shock show that the main failure styles of the coatings are crack and desquamation and the thermal shock resistance of the coatings is improved obviously by increasing the number of coating layers.


2009 ◽  
Vol 79-82 ◽  
pp. 775-778 ◽  
Author(s):  
Hong Li Liu ◽  
Chun Ying Tian

The self-healing ceramic coating against oxidation for carbon/carbon composite was fabricated via preceramic polymer pyrolysis process using polysilazane as preceramic and MoSi2, B4C powders as fillers. By means of SEM and XRD, the phase compose and microstructure of coating were characterized, and preliminarily study on its anti-oxidation ability and thermal shock resistance were conducted. The results showed that, the coating is composed of the resisting oxidation layer and the sealing layer. The thickness of the coating is about 50μm, and the coating is uniform and densified. Good contact at the interfaces is visible on the SEM photograph. At 1300°C temperature, the thermal shock resistance test was conducted 50 times, the weight loss rate was 2.12%. In range of 1200°C~1500°C, the anti oxidation ability of the coating is good.


2011 ◽  
Vol 250-253 ◽  
pp. 588-594 ◽  
Author(s):  
Dong Wang ◽  
Yong Li ◽  
Yang Li ◽  
Rui Li ◽  
Yue Li

Using high pure magnesia and magnesia-spinel as the main raw material, keeping the same quantity of spinel, specimens were made with different spinel size distribution (≤0.044mm, 1-0mm, 2-1mm, 3-2mm and 3-1mm). Dextrin and brine are the binder. Specimens were dried at the temperature of 110°C for 24 hours, sintered at the temperature of 1680°C holding 8 hours in a tunnel kiln. The properties and microstructure of the specimens were analyzed. The results are shown that the addition of spinel with grain size of 3-1mm improves sintering of magnesia-spinel brick, with the thermal shock resistance reaching 18 cycles, the cold crushing strength reaching 54 MPa, improving the comprehensive performance of the magnesia-spinel brick.


2017 ◽  
Vol 36 (3) ◽  
pp. 844-848
Author(s):  
FA Ovat ◽  
DE Ewa ◽  
EA Egbe

The characterization of some clay as refractory materials for furnace lining has become relevant to find solutions to the cost involved in the purchase and importation of these refractory materials. This work investigated the refractory properties of clay samples for their suitability for use in the industries. Clay samples were collected from Gakem and Abouchiche areas and analysed for physical and chemical properties to determine the suitability of the clays as refractory materials. The results showed cold crushing strength (21.46MN/m2), thermal shock resistance (27 cycles), bulk density (3.52g/cm3), linear shrinkage(3.80%), apparent porosity (28.84%) and permeability (80%) for Gakem; and cold cold crushing strength (18.40MN/m2), thermal shock resistance (25 cycles), bulk density(2.81g/cm3), linear shrinkage (3.70%), apparent porosity (25.86%) and permeability (77%) for Abouchiche respectively. The chemical compositions of these clay samples were also investigated. The results showed that the samples fall under Aluminosilicate type of clay because of their high values of Aluminium Oxide and Silicon Oxide. Tests showed that clay from these areas can be used to produce refractory materials that can withstand a furnace temperature of about 1600°C. http://dx.doi.org/10.4314/njt.v36i3.26


2013 ◽  
Vol 315 ◽  
pp. 11-14 ◽  
Author(s):  
I.A. Rafukka ◽  
B. Onyekpe ◽  
Y. Tijjani

The investigations centered on how addition of Gezawa clay (GC) affects the refractory properties of the Gezawa stone (GS) (Silica Stone) with a view to finding the optimum percentage of the blend that will give good refractory properties. The samples were crushed, ground, sieved and the chemical compositions were determined. Test samples were produced by blending the Gezawa stone with various proportions of Gezawa clay. The refractoriness of the samples was measured, and the samples were then fired to 1100and standard properties such as thermal shock resistance, cold crushing strength and apparent porosity were determined. The result shows that addition of Gezawa clay to Gezawa stone improves its thermal shock resistance but reduces the refractoriness, while the porosity was found to be within the specified range for fire clay and the cold crushing strength of the samples was high. Compromise could be made in selecting the percentage that would suit certain application.


2013 ◽  
Vol 6 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Abdulmula Ali Albhilil ◽  
Martin Palou ◽  
Jana Kozánková

Abstract Series of six cordierite-mullite ceramics were synthesized via solid state reaction at various temperatures from 1250 °C for pure cordierite to 1500 °C for pure mullite. Then the samples were submitted to the test of thermal shock resistance based on cycling heating-quenching procedure. X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Mercury intrusion porosimeter (MIP) have been used to characterize the samples before and after cycling heating-quenching method. Sample 6 was broken after 35 heating-quenching cycles, while the five other reminded stable. The refractoriness of samples is found to be higher than that of commercial ones. XRD shows that heating-quenching procedure has led to crystallization of cordierite and mullite phases. Apart from sample 6, the pore structure is stable with slight consolidation. The microstructure images confirm the results of XRD and MIP showing crack in sample 6 only, but compact and larger particles resulting from crystal growth in other samples due to the repeated action of heating.


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