Abstract: Α-Al2O3 Films Were Prepared by Laser Chemical Vapor Deposition and the Effects of Precursor Evaporation Temperature (Tvap) and Oxygen Gas Flow Rate (FRo) on Phase and Orientation of Al2o3 Films Were Investigated. at Tvap = 413 K, (100)-Oriented α-Al2O3 and θ-Al2O3 Were Codeposited. the Amount of θ-Al2O3 Increased with Increasing FRo. at Tvap = 433–443 K, α-Al2O3 Films Showed a (001) Orientation. (100)- and (001)-Oriented α-Al2O3 Films Had a Rectangular- and Hexagonal-Shaped Grains, Respectively, and Showed a Columnar in Cross Section. Grain Size of (100)- and (001)-Oriented α-Al2O3 Films Decreased from 10 to 2 μm with Increasing FRo from 0.085 to 0.85 Pa m3 s−1. Deposition Rate Increased from 100 to 300 μm h−1 with Increasing Tvap from 413 to 443 K.
Abstract: Structures to Be Based on Hafnium Dioxide Are Regarded as the Most Perspective High-K Dielectric for Integration in MOS-Technology, Carbon Nanotubes Transistors. MOCVD (Metal-Organic Chemical Vapor Deposition) Techniques of HfO2, Al2O3 and (Al2O3)x(HfO2)1-X Thin Films Were Applied Using Metal-Organic Substances as the Precursors. Dependences of Growth Rates on Process Parameters Were Studied. The Chemical Structure and Properties of the Films and Electrophysical Characteristics of the Test Structures Were Investigated.
Abstract: Sino Fibers Reinforced BN Wave-Transparent Composites (SiNOf/BN) Were Fabricated through Precursor Infiltration and Pyrolysis (PIP) Method Using Borazine as Precursor. The Effect of Pyrolysis Temperature on the Densification Behavior, Microstructures, Mechanical Properties and Dielectric Properties of the Composites Was Investigated. The Results Suggest that with the Increase of the Pyrolysis Temperature from 800 °C to 1000 °C, the Density, Mechanical Properties and Dielectric Constant of the Composites Are Increased, but the Infiltration Efficiency Varies Little. At the Pyrolysis Temperature of 1000 °C, the Density of SiNOf/BN Composites is 1.84 g∙cm-3 and the Flexural Strength and Elastic Modulus Are 148.2 MPa and 26.2 GPa Respectively. The Dielectric Properties, Including Dielectric Constant of 3-4 and Dielectric Loss Angle Tangent of below 7×10-3, Obtained at Three Different Temperatures Are Excellent for the SiNOf/BN Composites Applied as Wave-Transparent Materials.
Abstract: SiAlON Was Mixed with Ni Nanoparticle Precipitated cBN (SiAlON-cBN/Ni) and Sintered by Spark Plasma Sintering at 1923 K for a Holding Time (tH) of 0 to 1.8 Ks. the Effect of Ni Nanoparticle and Holding Time on the Phase Transformation of cBN to Hexagonal (hBN), Densification, Microstructure and Hardness of the SiAlON-cBN Composites Was Studied. At tH =1.8 Ks , the Relative Density of the SiAlON-20 Vol% cBN/Ni Was 99%, 7% Higher than that of SiAlON-20 Vol% cBN, Indicating that Ni Nanoparticle on cBN Promoted the Densification of SiAlON-cBN Composites. The BN Grains in SiAlON-20 Vol% cNB Showed a Round Morphology, whereas the BN Grains in SiAlON-20 Vol% cBN/Ni Composite Showed a Flake Morphology Characteristic of hBN. The Phase Transformation of cBN Was Accelerated by Ni. the Maximum Hardness of SiAlON-20 Vol% cBN/Ni Was 16.3 GPa Obtained at tH = 0 Ks.
Abstract: In this Paper, Five Fundamental Effective Thermal Conductivity Structural Models (Series, Parallel, Two Forms of Maxwell-Eucken and Effective Medium Theory) Were Used to Analyze and Design Silicon Nitride Porous Ceramics. Then α-Si3N4 Matrix Porous Ceramics Were Prepared with ZrP2O7 as a Binder and Thermal Conductivity of ZrP2O7 Bonded Si3N4 Porous Ceramic Was Evaluated. ZrP2O7 Bonded Si3N4 Porous Ceramic Had Open and Interconnected Pore Structure which is either in EMT or in Maxwell-Euken 2. The Thermal Conductivity of ZrP2O7 Bonded Si3N4 Porous Ceramics Changes from 2.0 to 0.5 W/m•K with Increasing the Porosity from 20% to 51%. The Obtained Results Showed that the External Porosity Material with Maxwell-Euken 2 Structure Had the Lowest Thermal Conductivity in All Porous Materials. The Open and Interconnected Pore Structure of ZrP2O7 Bonded Si3N4 Porous Ceramics Provided much Lower Thermal Conductivity.
Abstract: Nano-Sized ZrO2 Powders Were Synthesized from ZrOCl2•8H2O by Polyvinyl Alcohol-Gel Technology, Using Polyvinyl Alcohol (PVA) as a Monomer and Glutaraldehyde (GA) as a Cross-Linking Reagent. The Stability of the Gel Was Affected by Concentration of PVA and GA, Volume of ZrOCl2•8H2O. Moderate Strength of Gel Was Synthesized by Raw Materials of PVA (2%), ZrOCl2•8H2O (30~40 g) and GA (10ml). Nano-Sized ZrO2 Was Obtained Finally, with Uniform Particle Size and Good Dispersibility, and Size Was about 20 nm. Doped ZrO2 with Stabilized Tetragonal Crystal Was Obtained at Room Temperature. The Effect of Calcine Temperature on Phase Structure of ZrO2 Powders Has Been Investigated.
Abstract: The Nearly Full Dense Zr2Al3C4 Ceramic Was Successfully Fabricated at 1800 °C for 10 min under a Uniaxial Load of 20 MPa in Vacuum by the Spark Plasma Sintering Process, Using a Mixture of Zr, Al and Graphite Powders as Raw Materials. The Reaction Route of Synthesis as Well as the Sintering Conditions of the SPS Technique Were Discussed Based on X-Ray Diffraction Results. The Results Showed that the Heating Rate Can Largely Affect the Loss and Aggregation of Molten Al. Moreover, the Contents of Al4O4C and the Elevated Sintering Temperature Were Beneficial for the Synthesis of Zr2Al3C4 Ceramic. The Microstructures of the Samples Were Observed by Scanning Electron Microscopy, Showing that the as-Synthesized Zr2Al3C4 Has an Anisotropic Microstructure Consisting of Elongated Grains. Compared to the Hot-Pressing, the Starting Temperature for the Formation of Zr3Al3C5 and Al4O4C Phases Was Rather Low. It Indicates that the SPS Technique Can Rapidly Synthesize Zr2Al3C4 from the Zr/Al/C Powders in a Relatively Low Temperature Range. The Mechanical Properties of the Sintered Materials Were Also Investigated, Including the Hardness of 11.66±0.34 GPa, and Fracture Toughness of 4.0 ± 0.4 MPa×m1/2.
Abstract: Sintering Behavior of Monolithic TiN and TiB2 Was Investigated Using Spark Plasma Sintering (SPS) at Temperatures between 1673 and 2573 K. Relative Density of TiN Was Increased from 82.3 to 96.7% while that of TiB2 Increased from 70.1 to 92.8% with Increasing Temperature. At Temperatures between 1673 and 2273 K, TiB2 Was More Difficult to Consolidate Compare to TiN. At 2473 K, TiB2 Densified Rapidly to 92.8%.
Abstract: In this Study, a Good Combination between Si3N4-Based Seal Coatings and Porous Si3N4 Substrate Was Achieved by Room Temperature Spraying and Pressureless Sintering. To Evaluate the Joint Quality, Residual Stress due to Thermal Expansion Mismatch between the Coatings and Porous Layers Were Characterized by Computational Studies Using the Finite Element ANSYS Code. It Was Found that Si3N4-Based Seal Coating Allows a Gradual Change in Thermal Expansion Mismatch, Minimizing the Thermal Stresses Arising from Cooling or Heating. Further Theoretical Analysis Indicates that the Thermal Expansion Mismatch between the Two Layers Produced a Large Strengthening Effect for the Fraction of the Porosity below a Critical Level and that Substrates with the High Fraction of Porosity Showed Complete Cracking, as the Cracks Initiating in Adjacent Coatings. And the Volume Fraction of Pores Required to Cause Crack Deflection, in the Porous Layer, Was Predicted. The Effects of Layer Thickness and Porosity Fraction on Residual Stress Were Studied, which Are Used as Predictions towards Better Design of Composite Materials.