Influence of CAD-CAM milling on the flexural strength of Y-TZP dental ceramics

In this work, the influence of milling strategy and cutter wear on the flexural strength of sintered Y-TZP ceramics machined in a CAD-CAM system, was investigated. Pre-sintered Y-TZP blocks were machined with tungsten carbide (WC) milling cutters and divided into three groups: a) samples machined with New Cutting Tools (NCT); b) samples machined with End-of-life cutting tools (ELCT); and c) samples machined and subsequently polished. The samples were machined parallel and perpendicularly to the diameter of pre-sintered Y-TZP blocks aiming to evaluate the effect of the machining orientation on roughness. After cutting, the specimens were sintered at 1530?°C for 2?h and characterized. After sintering, dense Y-TZP samples presenting grain size average of 0.81?±?0.23?μm, hardness of 1205?±?12 HV, K_C of 7.7?±?0.4 MPam^1/2 and flexural strength of 1207?±?199?MPa were obtained. Furthermore, the control roughness (polished surfaces) presented R_a?=?0.058?±?0.011?μm. The surface roughness of the samples was influenced by the machining methodology using NCT mills, with R_a?=?0.386?±?0.149?μm and R_a?=?0.292?±?0.105?μm for samples machined parallel and perpendicularly to the pre-sintered Y-TZP blocks, respectively. The use of ELCT led to a roughness increasing (R_a?=?0.582?±?0.183?μm for samples milled perpendicularly, and R_a?=?0.919?±?0.164?μm for samples cut parallel to the pre-sintered blocks. The flexural strength of the sintered Y-TZP decreases with use of ELCT as consequence of surface roughness increasing, resulting from wear of WC mills, which presented chippings with sizes ranging from 30 to 340?μm in the cutting edge.     

Influence of fluorine source and TiO2 on glass ceramics based on red clay and magnesite

Abstract

Within the Fe₂O₃–BaO–Al₂O₃–SiO₂ glass system, the influence of different fluorine source and TiO₂ on the crystallisation behaviour and thermal expansion characteristics has been investigated. These aluminosilicate glasses, with different nucleation catalysts (TiO₂, AlF₃ and NH₄F), were successfully prepared from Saudi Arabia raw materials (red clay and magnesite). Thermal behaviour, crystalline phases, microstructures, and thermal expansion coefficient were studied by DTA, XRD, SEM techniques, as well as a dilatometer. Spinel, hexacelsian, monocelsian, kinoshitalite, and Ba-osumilite were developed in glass ceramic samples. Spinel was the early phase formed in all glasses; however, with increasing temperature, hexacelsian and kinoshitalite were developed in fluorine free glasses and fluorine containing glasses respectively. Ba-osumilite was developed and hexacelsian was converted into monocelsian during lengthy heat treatment at 1150°C. A bulk crystalline microstructure was obtained; however, a microscale structure was observed in fluorine free samples and a homogeneous nanoscale microstructure was developed in fluorine containing samples. The coefficient of thermal expansion (CTE) varied according to the phases and the heat treatment parameters. Development of spinel, hexacelsian and kinoshitalite in glass ceramic samples gave CTE values between 86·44 × 10^?7 and 52·53 × 10^?7°C^?1, whereas crystallisation of Ba-osumilite and monocelsian gave CTE values between 51·29 × 10^?7 and ?7·35 × 10^?7°C^?1.     

Influence of LaF3 on the crystallization and luminescence of Eu-doped oxyfluoride glass ceramics

The influence of LaF₃ on the crystallization behavior and luminescence of Eu³⁺ ions in the oxyfluoride borosilicate glass ceramics was investigated in details. Differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) results indicated that the addition of LaF₃ decreased the glass transition temperature and promoted the crystallization of BaF₂ nanocrystals, which distributed homogeneously in the glassy matrix. A reduction of the lattice parameters of BaF₂ nanocrystals, the obvious Stark splitting of emission peaks and long fluorescence lifetime evidenced the incorporation of Eu³⁺ and La³⁺ into the BaF₂ lattice. Furthermore, experimental results indicated the distribution of Eu³⁺ ions in the oxyfluoride glass ceramics may be modified by the addition of LaF₃ content.     

Diopside–Ca-Tschermak clinopyroxene based glass–ceramics processed via sintering and crystallization of glass powder compacts

The suitability of three new glass compositions for producing diopside–Ca-Tschermak clinopyroxene based glass–ceramics (GCs) was investigated. With respect to the formula of diopside, the first investigated composition resulted from the substitution 0.2(Si⁴⁺ + Mg²⁺) ↔ 0.4 Al³⁺, which leads to a composition of 80 mol.% diopside and 20 mol.% Ca-Tschermak. The substitutions in the second compositions were 0.25(Ca²⁺ + Si⁴⁺) ↔ 0.25(Y³⁺ + B³⁺) and 0.2(Si⁴⁺ + Mg²⁺) ↔ 0.4Al³⁺, and in the third composition 0.2Ba²⁺ ↔ 0.2Ca²⁺ and 0.2(Si⁴⁺ + Mg²⁺) ↔ 0.2(B³⁺ + Al³⁺). The influence of these substitutions on glass crystallization and the properties of the GCs produced between 850 and 1000 °C was experimentally investigated. The experimental results showed that the easily cast glasses, after melting at 1580 °C for 1 h, are prone to surface crystallization. Augite is predominantly crystallized, but Ca- and Ba-aluminosilicates can also form, according to the substitutions. The stability of the assemblage of the crystalline phases over a wide temperature range (850–1000 °C) and prolonged heat treatment (up to 50 h) and the properties of the produced GCs indicate a high potential of these compositions for several functional applications.     

Factors that influence the flexural strength of SiC-based porous ceramics used for hot gas filter support

The influences of molding pressures, bonding phase contents, and SiC particle sizes on the flexural strength of SiC-based porous ceramics were investigated based on their microstructure of fracture surface. The SEM morphologies and EDS element analysis results of fracture surface showed that there were two different kinds of fracture points: SiC particle fracture points and bonding phase fracture points. It is found that molding pressures, bonding phase contents, and SiC particle sizes affect the SiC particle fracture point area in the fracture surface, and the fraction of the SiC particle fracture point area in the minimum solid area of fracture surface is a determined influence factor for the flexural strength of SiC-based porous ceramics used for hot gas filter support.     

TiO_2含量对聚酯切片结晶性能的影响

TiO2粒子作为消光剂存在于聚酯的非晶区中,对聚酯结晶过程有显著影响。在聚酯切片的冷结晶过程中,由于吸附及空间位阻作用,对结晶起阻碍作用;在聚酯熔融结晶过程中,作为晶核,对结晶起促进作用。w(TiO2)DSC参数表明:玻璃化转变温度tg、冷结晶峰温tc、熔融结晶峰温tmc随w(TiO2)降低而下降。     

Effect of Cr2O3 on the crystallization behavior of synthetic diopside and characterization of Cr-doped diopside glass ceramics

Diopside is the main crystalline phase in silicate materials such as ceramics and glass-ceramics. Herein, the effect of Cr₂O₃ on the microstructure and crystallization behavior of synthetic diopside, as well as the solubility of Cr₂O₃ in diopside is discussed. Samples were prepared by the melting method and characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, and confocal laser scanning microscopy. Results show that the maximum achievable solubility of Cr₂O₃ in diopside is between 1% and 3% by weight, and that the magnesiachrome spinel formed by Cr₂O₃ can act as a nucleating agent for the diopside phase. Glass ceramics was prepared by synthesis slag which simulates the chromium-containing waste. The activation energy of crystallization is 274 KJ/mol and Avrami parameter is 3.23. The leaching behavior of glass ceramics was studied. Additionally, the effect of Cr₂O₃ on the mechanisms of phase change were discussed. The study provides a theoretical basis for the preparation of chromium containing waste-based silicate materials with diopside as the main crystalline phase.     

Effect of water and isooctane absorption on the flexural fatigue strength of a sheet molding compound

The effect of water and isooctane absorption on the flexural fatigue strength of a sheet molding compound (SMC-R30) is investigated. Absorption of water reduces the fatigue life of specimens of SMC-R30 as compared to the fatigue life of specimens tested in air. Absorption of isooctane reduces the fatigue life much more than absorption of water.     

无机粒子含量对聚酯切片结晶性能的影响

运用差示扫描量热法(DSC)对含A种无机粒子聚酯(PET)的结晶性能进行表征。研究表明:不同A含量的聚酯在所研究的含量范围内,随A含量升高,聚酯的玻璃化转变温度Tg无明显变化,冷结晶温度Tc呈升高趋势,熔点Tm呈升高趋势,熔融结晶Tmc呈降低趋势,过冷度△Tmc呈增大趋势,半结晶周期t1/2呈增加趋势。