Electroless Ni–P Plating on Mullite Powders and Study of the Mechanical Properties of Its Plasma-Sprayed Coating

To effectively improve the properties of a mullite coating and its interfacial bonding with the substrate, a Ni–P layer is deposited on the surface of mullite powders by electroless plating. The original mullite powders and coated mullite powders are then deposited onto stainless-steel substrates by plasma spraying. The growth mechanism of the Ni–P layer during the plating, the microstructures of the coated powders and mullite coating and the properties of the mullite coatings are characterized and analyzed. The results indicate that the Ni–P layer on the surface of the mullite powder has cell structures with a dense uniform distribution and grows in layers on the surface of the mullite powder. The crystallization behavior of Ni-P amorphous layer is induced by heat treatment. Compared to the original mullite coating, the coating prepared by the coated mullite powders has better manufacturability, stronger adhesion to the substrate, lower porosity (7.40%, 65% of that of the original coating), higher hardness (500.1 HV, 1.2 times that of the original coating), and better thermal cycle resistance (two times that of the original coating). The method of preparation of high-temperature thermal barrier coatings with coated mullite powders has a high application value.

Synthesis and Characterization of Mullites From Silicoaluminous Fly Ash Waste

Fly ash is considered one of the major hazardous pollutants around the globe. Every year a million tonnes of fly ash is disposed of into the fly ash ponds which are major sites of pollution. The major fractions of fly ash are silicates, aluminates, and ferrous substances followed by minor traces element oxides. The aluminates and silicates comprise of 70% of the fly ash. The aluminates and silicates are present in fly ash in the form of crystalline mullites and sillimanites. Mullites being inert and crystalline are retractile to mineral acids. So, here the authors have reported a novel and simple step for the recovery of all the major elements of fly ash along with recovery of mullites by using hydrofluoric acid at room temperature. The method comprises of treatment of fly ash with diluted hydrofluoric acid for 12 hours under agitation. The recovered white color mullite powder, rod shaped of size 90-300 nm, was analyzed by the sophisticated instruments for the confirmation of the mullite particles.

Application of Statistical Analysis in the Powder Injection Molding (PIM) of Mullite

In this work, the statistical analysis methods, including least square method and statistical hypothesis testing, were used to study the flexural strength and density of the specimens formed from mullite powder by powder injection molding (PIM). The feedstock for PIM consist of mullite powder and the composite binder consisting of 78 wt% polyethylene glycol (PEG), 20 wt% polyvinyl butyral (PVB), and 2 wt% stearic acid (SA). The PIM machine used in this work was the lab-scale plunger type. The compositions of the feedstock that could be injection molded by this machine were 50, 52, and 54vol% mullite. After molding, PEG in the green specimens was removed prior to sintering by soaking the specimens in the water at 60 °C for 24 hours while PVB and SA were removed during sintering. The sintering temperatures were 1300 to 1450°C. At significance level of 0.05, the least square method and the statistical hypothesis test showed that both feedstock compositions and sintering temperatures used in this work affected the densities of sintered specimens. However, the increasing of the flexural strength of sintered specimens was mainly by the increasing of the sintering temperature.

Influence of Pulse Frequency on Mullite Coatings Prepared by Pulse Arc Discharge Deposition Process and Activation Energy

Mullite coatings were prepared on C/C-SiC composites surface by pulse arc discharge deposition using mullite powder as source materials. Phase composites and microstructures of the as-prepared mullite coatings were characterized by XRD and SEM. Deposition kinetics and influence of pulse frequency on the phase composites and microstructures were investigated. The results indicate that the outer layer is composed of mullite phase, density and homogeneity of the mullite coatings are achieved when the pulse frequency reaches 2000 Hz. The deposition amount of the mullite coatings also increases with increasing deposition temperature. The deposition mass of the coatings and the square root of the deposition time at different deposition temperatures according to linear relationship, and the deposition activation energy is calculated to be 32.24 kJ/mol.

Highly selective enrichment of phosphopeptides using aluminum silicate

This study presents a novel strategy for highly selective enrichment of phosphopeptides using aluminium silicate (mullite) powder.

Preparation of Porous Mullite Ceramics with Low Thermal Conductivity

Porous mullite ceramics were prepared using an industrial grade mullite powder by foaming and starch consolidation method. The influence of solid loading of suspension and sintering temperature on the porosity of samples was evaluated. The sintered mullite ceramic with porosity from 73 to 86 vol% contained the microstructure with spherical pores and a larger mean pore size. Thermal conductivity measurements were carried out by the hot-disk technique at room temperature resulted in values as low as 0.09 W/(m·K).

Study on Preparation of Mullite Powder Using Fly Ash by Mechanochemical Method

This paper studies the structural changes of the mixture of fly ash and A12O3 grinded by planetary ball mill . By investigating the structure of the ground product by SEM, XRD and FT-IR, the mechanism of mullite formation is discussed. The crystal structure of the mixture was destroyed by the grinding of planetary ball mill, and with the grinding time increases, the specific surface area of the mixture increases as well. And this leads to the decrease of bond energy, the increase of the internal energy and the decrease of the activation energy. After this process,uniform mixture and direct formation of signal phase mullite can be obtained from the mixture grinded for 30 hours and calcined at 1150°C for 2 hours and the temperature for mixture ungrinded needs to reach 1450°C.

Research on enhancement of GFRP-anchor’s torsional strength

This article mainly aims at experiments to modify the matrix phase in glass fiber-reinforced plastics anchor (GFRP-anchor), trying to achieve the enhancement in the torsional performance of GFRP-anchor in order to expand its application field. The experiments were to add the mineral filling nano mullite powder and the toughening agent acrylic-polyurethane emulsion with different proportions into the matrix phase which experienced a vacuum-pumping process for the removal of bubble, while the same reinforced phase glass fiber was used by all the GFRP-anchor samples with the same forming process conditions. Torsion test and scanning electron microscopy (SEM) observations were investigated, and the results revealed that adding nano mullite powder into the matrix phase as the mineral filling with the mass fraction ratio of 1.5%, the acrylic polyurethane emulsion as the toughening agent with 5%, as well as the vacuum-pumping process for the removal of bubble from the matrix phase, can greatly improve the torsional strength of the GFRP-anchor by 35%, 41%, and 51%, respectively.