Papers by Author: Lin Jiang Wang

Abstract: The joining of high temperature structural ceramics to other materials is an important process commercially and technologically. Due to the existence of physical and economic limitations for the manufacture of large parts, joining is essential. Functional gradient materials (FGMs) are designed to exhibit a desirable gradient in a property, due ether to a gradient in composition, or microstructure, or both. In this paper, Si3N4-Al2O3 functional gradient joining material was prepared by hot press sintering of multilayered FGMs with 20 layers of thickness 400um each using β-Sialon as transient interlayer. The structure and properties of the materials were analyzed by the means of scan electron microscopy(SEM), X-ray diffraction(XRD) and micro-sclerometer. The components of the materials have gradient distribution and successional. The microhardness is gradient changing with the change of micro-structure. The interface between layers is tightly coupling and has no stress convergence. The test of thermal shock and fatigue cracks of FGM between 1300 °C and 900 °C show good properties of thermal stress relaxing and resistance for high temperature.

Abstract: Multilayered mullite/Mo cermet functionally gradient material (FGM) was fabricated through a powder stacking process and sintering in vacuum up to 1500°C. The composition distribution, microstructure and microhardness of the FGM were analyzed. The results indicated that the mullite/Mo FGM was well densified with composite graded distribution and there was no new phase appeared. The microhardness of the FGM increase from 467HV to 1543HV, the density from 2.919 to 7.106 g/cm3 as the content of mullite increase from 20% to 80%. The relative density exceeded 90% as the content of mullite reached 80%. Thermal shock test showed that the cracks passed through the joint without deflection.

Abstract: Kaolinite-glucose intercalation compound was synthesized by the intercalation of polar organic big molecule dodecylamine and then displaced by glucose in the layer of kaolinite. XRD, FT-IR, TG and DSC were used to study the reaction process and the characters of the products. The results indicated that the basal spacing of kaolinite increased to 2.280 nm from 0.717 nm, and the hydrogen bonds were formed between dodecylamine NH and kaolinite Si-O after dodecylamine intercalation. Kaolinite-dodecylamine intercalation compound was stable below 295 °C. After displacement reaction by glucose, the basal spacing of kaolinite increased to 3.364 nm, and the intercalation rate reached 87%, the hydrogen bonds were formed between glucose C=O and kaolinite inner surface hydroxyl. Kaolinite-glucose intercalation compound was stable below 302 °C.

Abstract: Porous silica was prepared by selective leaching of metakaolinite with 20 mass% HCl solution. The metakaolinite was derived from the 1:1 layered structure clay mineral kaolinite by firing at 600°C for 24 h. The characteristics of porous silica were studied. The content of Al2O3 in metakaolinite was sharply changed from 45% to less than 2% after 2 h leaching. The maximum specific surface area of the leached sample was about 350 m2/g. The average pore size is about 2 nm. The total pore volume is 0.3 ml/g. The layer structure of kaolinite and metakaolinite is responsible for forming micropores.

Abstract: Kaolinite/formamide intercalation materials are characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy(FT-IR), Raman spectroscopy and 1H magic angle spinning nuclear magnetic resonance spectroscopy (1H MAS NMR). The d(001) spacing of kaolinite treated with formamide is 1.020nm, which is larger than that of the original clay. The 1H MAS NMR graphs show that the proton chemical shifts of the inner hydroxyl and inner surface hydroxyl of kaolinte are δ-1.3 and δ2.4 respectively. After formamide intercalation, the proton peaks of the inner surface hydroxyls shifted to high-field with δ2.3, the proton peak of the inner hydroxyl shifted to δ-0.3 toward low-field. In the hydroxyl stretching vibration region of Raman spectrum, the formamide intercalation resulted in the decrease of the intensities of kaolinite inner surface hydroxyl bands at 3699cm-1,3682cm-1, 3665cm-1 and 3642cm-1, and the appearance of additional bands at 3610cm-1,3628cm-1. In the NH stretching region of FT-IR spectrum, two bands are observed at 3336cm-1 and 3466cm-1 corresponding to the two types of the hydrogen bonds between formamide and kaolinite. In the carboxyl stretching region, an additional band at 1667cm-1 is assigned to C=O group that bonded to the inner surface hydroxyl of kaolinite.

Abstract: X-ray diffraction (XRD) method to measure the residual stress existing in the metal substrate surface layer was introduced and the sol-gel ZrO2-CeO2 thin film was successfully prepared on SUS304 stainless steel substrate by dip-coating process. The macro residual stress existing in metal substrate was analyzed by XRD. It turns out that the compressive stress existing in the metal substrate surface layer increases with the increase of heat-treated temperature. Based on the above study, colored stainless steels of high quality were prepared by sol-gel process.

Abstract: The kaolinite-polyacrylamide intercalation compound was prepared by the displacement reaction of the kaolinite-formamide intercalation precursor with acrylamide and the polymerization under 140°C for 15h with the catalysis of dibenzoyl peroxide. Sialon was synthesized from kaolinite-polyacrylamide intercalation compound by carbothermal reduction and nitridation (CRN) processing at 1400°C. The kaolinite-carbon mixture and its CRN product were also prepared for the comparison with the CRN result of intercalation compound. XRD, FT-IR, and TEM were used to characterize the phases, structure and morphology of products. In the CRN product from the intercalation compound, β′-sialon is the main phase. And the reduction and nitridation rate from the intercalation compound was greater than that from the mixture. There was higher sialon phase’s content and lower mullite phase’s content in the CRN product from the intercalation compound than that from the mixture. The CRN processing of kaolinite intercalation compound is a novel and effective method of sialon synthesis.