Effect Of AlN Content Research Articles

The Effect of AlN Content on the Properties of Al2O3-AlN Composite Ceramics Fabricated by Digital Light Processing

In this work, Al2O3-AlN composite ceramics with high bending strength and thermal conductivity were fabricated by Digital Light Processing (DLP). The influence of AlN content on the rheological and cure behavior of Al2O3-AlN suspensions, as well as the microstructure, thermal conductivity, and bending strength of Al2O3-AlN ceramics, were systematically investigated. The result shows that the viscosity and cure ability of the suspensions were decreased with the increase of AlN content, which are beneficial to the spreading and printing accuracy of the suspensions. Besides, the bending strength of ceramics can be improved due to the residual stress by the introduction of AlN. Approaches were employed to minimize the formation of AlON in Al2O3-AlN ceramics by optimizing the amount of AlN and the sintering temperature. The thermal conductivity and bending strength of Al2O3-AlN ceramics were 31.72 ± 0.45 W/(m·K) and 572.73 ± 59.40 MPa, respectively, which are much higher than those of Al2O3 ceramics fabricated under the same condition. Finally, complex-shaped Al2O3-AlN ceramics components have been successfully fabricated by DLP, which may provide an opportunity to broaden the application of Al2O3-AlN composite ceramics in heat dissipation components.

Effects of AlN inorganic binder on the properties of porous Si3N4 ceramics prepared by selective laser sintering

Porous Si3N4 ceramics are widely used in the aerospace field due to its lightweight, high-strength, and high wave transmission. Traditional manufacturing methods are difficult to fabricate complex structural and functional ceramic parts. In this paper, selective laser sintering (SLS) technology was applied to prepare porous Si3N4 ceramics using AlN as an inorganic binder. And the effects of AlN content on the properties of the obtained ceramic samples were explored. As the AlN content increased, nano-Al2O3 and nano-SiO2 formed the eutectic liquid phase, enhancing the sintering densification and phase transformation of Si3N4 poly-hollow microspheres (PHMs). The island-like partial densification structures in Si3N4 green bodies increased. During the high-temperature sintering, the eutectic liquid phase partially transformed into the mullite phase or reacted with AlN and Si3N4 to form the Sialon phase. With the increase of AlN content, the fracture mode of Si3N4 ceramics changed from fracturing along PHMs to fracturing across PHMs. The bonding depth between PHMs increased and the connection between the grains was tighter, so the Si3N4 ceramics became denser. With the increase of AlN addition, the total porosity of the porous Si3N4 ceramics tended to decrease and the flexural strength gradually increased. When AlN content was 20 wt%, the total porosity and the flexural strength were 33.6% and 23.9 MPa, respectively. The addition of AlN inorganic binder was carried out to develop a novel way to prepare high-performance porous Si3N4 ceramics by SLS.

Effects of AlN Content and Sintering Atmospheres on the Thermal Conductivity of Hot-Pressed SiC Ceramics

In pursuit of high thermal conductivity of SiC ceramics, this article reports the effects of AlN and sintering atmospheres on the thermal properties and microstructure evolution of SiC ceramics. Dense SiC ceramics with different contents of AlN additive were fabricated through hot-press sintering at 1950°C in Ar/N2 atmosphere under a pressure of 40 MPa for 3 h. The results showed that the thermal conductivity of samples without AlN addition was 53.5 W.m−1.K−1 when sintered in Ar and 50.3 W.m−1.K−1 when sintered in N2. The SiC ceramics with 4 wt% AlN sintered in Ar showed abnormally large grains and exhibited the highest thermal conductivity of 121.7 W.m−1.K−1 among all the samples. The sample with 2 wt% AlN sintered in N2 exhibited a thermal conductivity of 108.6 W.m−1.K−1; the thermal conductivity deceased with the increasing AlN content afterwards. Such a decreasing trend of thermal conductivity was attributed to the ascending 2Hss content and smaller grains of ceramics. There existed an optimal content of AlN and a proper sintering atmosphere for perfecting the microstructure and the thermal conductivity of SiC ceramics.

Effect of AlN on microstructure, mechanical and thermophysical properties of NiAl/Fe based alloys prepared by vacuum hot-pressing sintering

The effect of AlN content on the microstructure and mechanical properties of NiAl/Fe–x AlN (x = 0, 3, 5, 10, 15 wt%) alloys were investigated after mechanical alloying with subsequent vacuum hot-pressing sintering. The results showed that the AlN reinforced NiAl/Fe alloy contained B2-ordered NiAl phase, Fe phase and AlN phase. As the AlN content increased, the density of the material decreased gradually, and the hardness and thermal conductivity increased greatly. NiAl/Fe based alloys with 5 wt% AlN obtained higher compressive strength and Rockwell hardness. When the content of AlN was 15 wt%, the density was 5.42 g/cm3, which was 18.6% lower than that of NiAl/Fe alloy. When the content of AlN was 5 wt%, the hardness reached the maximum value of 59.5 HRC, which was 69.04% higher than that of NiAl/Fe alloy. The thermal conductivity of the material first increased and then decreased with the increasing AlN content. When AlN content was 10 wt%, its thermal conductivity was higher than others at each temperature, and the maximum was 34.75 W/(m·k) at 600 °C in the study.

Effects of AlN content on mechanical and optical properties of AlON transparent ceramics

In this study, AlON powders with different AlN contents were synthesized by the carbothermal reduction nitridation method and used to prepare transparent AlON ceramics. Lattice parameters of AlON powders were calculated from XRD patterns to evaluate the effects on microstructure. The influences of the AlN content on the properties of the resulting AlON ceramics was investigated in aspect of density, mechanical properties and optical properties. With an increase in the AlN content, the density of the AlON ceramics increased, the grain size decreased, and the hardness and fracture toughness increased. Transparent AlON ceramics were obtained at the AlN content of 21.6–29.7 mol%. The refractive index of the AlON ceramics increased from 1.688 to 1.702 at 4000 nm with an increase of AlN content. The correlation between the composition and properties of the AlON ceramics obtained in this study will provide both theoretical and experimental reference for industrial AlON ceramic manufacturing.

Effects of AlN on the reactive sintering of porous Al2TiO5 composites

The porous Al2TiO5/Al2O3 composites were fabricated by reactive sintering at 1500–1700 °C in nitrogen atmosphere. The starting materials Al2O3 and TiO2 were mixed in an equimolar ratio and the addition of AlN was 5–40 mol%. The effects of AlN content and sintering temperature on phase composition, linear shrinkage, pore sized distribution, porosity and microstructure were investigated. The XRD results showed that the composites mainly consist of Al2TiO5 while the peak intensity of Al2O3 increased with AlN content. The median pore sizes decreased with increasing AlN content and were in the range of 2–6 μm, 1–2 μm, 0.4–0.7 μm, and 0.3–0.5 μm for composites using 10, 20, 30, 40 mol% AlN, respectively. The porosities of ATN10 and ATN20 were from 20% to 10% at 1600 °C to 1700 °C while the porosities of ATN30 and ATN40 were almost constant in between 11 and 13%. The addition of AlN effectively decrease the grain size of Al2TiO5 and led to reduce microcrack at the grain boundary.

Rapid synthesis of AlON powders by low temperature solid-state reaction

High synthesis temperatures and long soaking times are generally required to fabricate AlON powders, which can cause coarsening and aggregation of the powder. Solid-state reaction methods form AlON powders by a direct reaction of Al2O3 and AlN, enabling rapid synthesis of AlON powder at low temperatures. In this work, single phase AlON powders were fabricated by a solid-state reaction method using Al2O3 and AlN powders as raw materials. To lower the synthesis temperature and shorten the soaking time, the raw materials particle sizes and the homogeneity of the Al2O3/AlN mixture were investigated. The effects of AlN content, synthesis temperature, and soaking time on the synthesis of AlON powders were examined. When the AlN content was 27 mol%, single phase AlON powders were synthesized by calcining Al2O3/AlN mixture at 1680 °C for 20 min. After ball-milling at 250 rpm for 24 h, the synthesized AlON powder was ground into a single phase fine AlON powder with an average particle diameter of 320 nm, a narrow size distribution, and good dispersibility. Transparent AlON ceramics with dimensions of Φ100 mm × 1 mm were fabricated by pressureless sintering the produced fine AlON powder.

Three dimensional AlN skeleton-reinforced highly oriented graphite flake composites with excellent mechanical and thermophysical properties

To obtain light, strong materials with high thermal conductivity and low coefficient of thermal expansion (CTE), three-dimensional (3D) AlN ceramic skeleton reinforced highly oriented graphite flake (AlN/GF) composites were successfully prepared by combining vacuum filtration and spark plasma sintering. The effects of AlN content on the microstructure, mechanical and thermophysical properties of the composites were investigated. It was found that the introduction of AlN together with Y2O3 significantly promoted the densification and mechanical properties of the composites. The GF grains in the composites were highly oriented with the Lotgering factor >98%, and a 3D continuous ceramic skeleton was formed when the AlN content increased to 20 wt%. The formed ceramic skeleton tailors the thermophysical properties of the composites effectively. Particularly, the unfavourable high through-plane CTE (∼28 × 10−6 K−1) of highly oriented graphite matrix remarkably decreased to a low value (∼7 × 10−6 K−1) due to the thermal expansion constraint of the formed ceramic skeleton architecture. The 20 wt% AlN/GF composite possessed the best comprehensive properties with the bending strength >80 MPa, high in-plane thermal conductivity of 442 W m−1 K−1 and low through-plane CTE value of 7.3 × 10−6 K−1. Our strategy would facilitate the practical application of graphite-based composites in current demanding thermal management.

Effect of AlN content on the lattice site location of terbium ions in AlxGa1−xN compounds

Terbium lattice site location and optical emission in Tb implanted AlxGa1−xN (0 ≤ x ≤ 1) samples grown by halide vapour phase epitaxy on (0001) sapphire substrates are investigated as a function of AlN content. The samples were implanted with a fluence of 5 × 1014 cm−2 of terbium ions and an energy of 150 keV. Lattice implantation damage is reduced using channelled ion implantation performed along the 〈0001〉 axis, normal to the sample surface. Afterwards, thermal annealing treatments at 1400 °C for GaN and 1200 °C for samples with x > 0 were performed to reduce the damage and to activate the optical emission of Tb3+ ions. The study of lattice site location is achieved measuring detailed angular ion channelling scans across the 〈0001〉, and axial directions. The precise location of the implanted Tb ions is obtained by combining the information of these angular scans with simulations using the Monte Carlo code FLUX. In addition to a Ga/Al substitutional fraction and a random fraction, a fraction of Tb ions occupying a site displaced by 0.2 Å along c-axis from the Ga/Al substitutional site was considered, giving a good agreement between the experimental results and the simulation. Photoluminescence studies proved the optical activation of Tb3+ after thermal annealing and the enhancement of the 5D4 to 7F6 transition intensity with increasing AlN content.

Fabrication and properties of cordierite based glass/AlN composites by sol–gel and pressureless sintering

In this study, the effect of AlN content on the crystallization behavior of cordierite based glass, was firstly investigated. Results show that μ-cordierite appeared in the composites with high AlN content even at high temperatures, which implied that the AlN may broad the crystallization temperature range of μ-cordierite and depress the transformation of μ→α-cordierite. The crystallization temperature of α-cordierite was about 980°C for the pure glass and the temperature increased with AlN content for composites, but the crystallization temperature of μ-cordierite had reverse trend. The composites owned excellent bending strength when the AlN content was 20wt%. With increasing of AlN content, the dielectric loss was increased which was caused mainly by the structural loss and the appearance of μ-cordierite, but the dielectric constant had crosscurrent. It was observed that the composites were beneficial in producing LTCC material which can be highlighted with high strength, low shrinkage and good dielectric properties at 1MHz.

Effect of AlN addition on the thermal conductivity of pressureless sintered SiC ceramics

Dense silicon carbide ceramics with 0.5–10wt% AlN additions were pressureless densified by two steps sintering using B4C and C as sintering additives. The effects of AlN content on density, microstructure and thermal conductivity of SiC–AlN composites were investigated. SiC ceramics can be well densified in the presence of AlN. The phonon scattering mechanism and the Klemens–Callaway theory were used to calculate the thermal conductivity evolution of SiC ceramics result from the dissolved Al and N atoms. The main reason for the degradation of thermal conductivities is the point defect scattering dominated by the differences in size and interatomic forces between impurity and host atoms.

Effect of AlN content on properties of hot-press sintered Sialon ceramics

This article concerns a hot-press sintered Sialon ceramic using Si3N4 and AlN as raw materials, Y2O3 and La2O3 as additives. The influences of AlN adding amount (5~30wt.%) on the sintered densification, phase compositions and microstructures are discussed. Results showed that the β-Sialon ceramic could be obtained by hot-press sintering of 95~80wt.% Si3N4, 5~20wt.% AlN and extra 5wt% Y2O3-La2O3 additives, while the excess of 25wt.% AlN would lead to the transformation from β-Sialon to α-phase. The relationships of AlN contents with bending strength and thermal conductivity of the sintered composites were also involved in the study. For the composition of 80wt.%Si3N4-20wt.%AlN, the sintered sample showed the fracture strength of 408MPa and the highest thermal conductivity of 34W/(m·K) which is 44.7% higher than that of the sample at an adding AlN content of 5wt.%.

Effect of AlN content on the performance of brominated epoxy resin for printed circuit board substrate

AbstractPolymer matrix composites, based on brominated epoxy, a type of material widely used in printed circuit boards (PCBs), as matrix and AlN particle as filler were prepared. The influences of AlN content on the mechanical, thermal, and electrical properties of the composites were investigated by uniaxial tensile test, TMA, thermal conductivity measurement, DMA, and dielectric properties measurement. It was found that the properties of composites monotonically varied with AlN content except that maximum tensile strength and strain of composites corresponded to a filler content of 10 wt %. The results of DMA also showed the AlN reinforcement was more pronounced above Tg, and the peak area of tan δ versus T curves decreased with AlN content, which implied the damping capacity of the composite gradually decreased. The increase in Tg and decrease in damping were probably due to strong interaction between the AlN and epoxy matrix inhibiting the mobility of the epoxy chain. In addition, different theoretical models reported in the literature were used to predict the E, CTE, k, and Dk, and compared with the experimental data. Finally, suitable models were recommended in the present materials system. For the significant improvement of performance of epoxy, we can conclude that these composite materials may be promising for PCB substrate. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1662–1674, 2007

Effect of AlN-content on the microstructure and fracture toughness of hot-pressed and heat-treated LPS–SiC ceramics

The influence of additive content on the microstructural development of hot-pressed and heat-treated LPS–SiC has been investigated using AlN–Y 2O 3 mixtures at a molar ratio of 80:20, varying the total amount from 5, 10, 15 to 20 wt.%. Specimen were hot-pressed at 1900 °C for 1 h in nitrogen atmosphere under an applied pressure of 25 MPa and subsequently heat-treated at 2000 °C for 1, 2, 4 and 8 h. It has been found that the transformation rate of β - into α-SiC is retarded by higher AlN-contents and the formation of the 6H α-SiC polytype is favored. Furthermore, grain growth during annealing is also effectively inhibited. While hardness remained almost unchanged, fracture toughness varied with additive content and/or duration of the heat-treatment. Fracture toughness increased during the first 1 or 2 h of annealing,depending on the AlN-content, and diminishing for more prolonged treatments. The maximum fracture toughness has been determined for samples containing 10 wt.% of additives, hot-pressed and annealed during 1 h.