Design guidelines for titania-silica-alumina ceramics with tuned anatase to rutile transformation

Titania-based ceramics with adjustable anatase-rutile fractions were obtained by milling of anatase, quartz and corundum precursors, uniaxial pressing and firing at 1100?°C. The influence of silica and alumina, combined with milling time and compaction pressure, was studied by design of experiments. The L9 orthogonal array with a three-level noise factor was employed. Firing of pure titania at 1100?°C yielded complete anatase to rutile transformation (ART), whereas stabilized samples show that an optimum amount of 9% silica and 33% alumina reduces phase transformation to only about 5?wt% rutile. An extended correlation matrix combined with analysis of variance (ANOVA) was applied to assess the combined effects of quartz, alumina, milling time and uniaxial compressing pressure on relative density, and anatase to rutile transformation. Results show absence of ART after milling, and controlled partial conversion of anatase to rutile after firing. Very good fitting was obtained by multivariate analysis on considering first and second order terms for dependence on silica contents and interactions between silica and each of the remaining factors, including milling time. This empirical dependence could be interpreted on a sound physicochemical basis, allowing the prediction of suitable compositions and processing conditions to obtain rutile-free samples by conventional ceramic processing, and to design ceramic samples with controlled fractions of anatase and rutile.     

Properties of Triaxial Porcelain Bodies: Interpretation of Statistical Modeling

The effect of raw materials type and content on the properties of clay–feldspar–quartz compositions was studied using the statistical design of mixture experiments. Based on wall and floor tile industrial practice, 10 mixtures of three raw materials were selected and processed. Characterization results were used to calculate statistically significant and valid regression equations, relating fired body properties with clay, feldspar, and quartz contents in the unfired mixture. Such statistical modeling is discussed against quantitative X-ray diffraction and scanning electron microscopy results. The glassy phase present was found to control the microstructure and the mechanical strength of the fired ceramic body.     

Processing and properties of tape-cast alumina/zirconia laminates composites

In the present work, laminar ceramic structures formed by layers of alumina and partially stabilized zirconia were fabricated by water-based tape casting. Rheological, physical and mechanical properties of slurries and laminates were evaluated. The laminates consisted of stacked alumina and zirconia green tapes produced by thermopressing. Pyrolysis was carried out at 450 °C and sintering at 1500 °C. The alumina/zirconia laminates were studied for a better understanding of the formation behavior and crack propagation at the laminate interface. The flexural strength values of laminates depend on the stress state on their surface. The laminates with the highest amount of zirconia layers presented low strength values (6.7 MPa), while the laminates with more alumina layers had a higher strength level (57.7 MPa). This is because these laminates have alumina layers on the surface which are in a state of residual compressive stress.     

Mortar composition defined according to rheometer and flow table tests using factorial designed experiments

This paper reports the effects of distinct contents of silica fume (SF), superplasticizer (SP) and water/binder ratio (W/B) in mortars. Samples with SF (0–10 wt%), SP (1.0–1.2 wt%) and W/B ratio (0.30–0.35) were produced. Flow table test and rheometry were used as parameters to formulate mortars by means of a factorial design experiment. Setting time, water absorption, apparent porosity and compressive strength of mortars at 28 days were also determined. Mortar formulations with lower fluidity are restricting when a rheometer was used. For higher torques, adjustments with the regressive equation of the Bingham model are less accurate, since the flow behavior is less constant. On the other hand, mortars with higher fluidity it is limited by spread test. The spread value on flow table test is more related to yield stress than to plastic viscosity. The design experiments identified the main factors (SF, SP and W/B) and their interactions for all properties on the fresh and hardened state, showing that experimental design with multiple regression equations is an appropriate tool to be applied in this case. Water content was the controlling parameter for practically all properties studied.     

Colloidal Processing of Glass–Ceramics for Laminated Object Manufacturing

Green tapes of Li₂O–ZrO₂–SiO₂–Al₂O₃ (LZSA) parent glass were produced by aqueous tape casting as the starting material for the laminated object manufacturing (LOM) process. The rheological behavior of the powder suspensions in aqueous media, as well as the mechanical properties of the cast tapes, was evaluated. According to ξ potential measurements, the LZSA glass powder particles showed acid surface characteristics and an IEP of around 4 when in aqueous media. The critical volume fraction of solids was about 72 wt% (27 vol%), which hindered the processability of more concentrated slurries. The glass particles also showed an anisometric profile, which contributed to an increase in the interactions between particles during flow. Therefore, the suspensions could not be processed at high solids loadings. Aqueous-based glass suspensions were also characterized by shear thickening after the addition of dispersants. Three slurry compositions were formulated, suitable green tapes were cast, and tapes were successfully laminated by LOM to a gear wheel geometry. A higher tensile strength of the green tapes corresponded to a higher tensile strength of the laminates. Thermal treatment was then applied to the laminates: pyrolysis at 525°C, sintering at 700°C for 1 h, and crystallization at 850°C for 30 min. A 20% volumetric shrinkage was observed, but no surface flaws or inhomogeneous areas were detected. The sintered part maintained the curved edges and internal profile after heat treatment.     

Predicting porosity content in triaxial porcelain bodies as a function of raw materials contents

This work describes the relationships observed between the porosity of fired ceramic test pieces and the raw materials contents in the unfired mixture. The investigation was carried out using the mixture experiments design approach coupled with response surface methodology, which enables the calculation of statistically significant models for the properties from a limited number of experimental results. Ten formulations of a clay mixture, potash feldspar and quartz sand were processed in the laboratory under fixed conditions, similar to those used on wall and floor tile industrial practice, and characterized. Closed porosity (CP) was estimated from the analysis of back-scattered SEM photomicrographs, open porosity (OP) was calculated as the product of bulk density and water absorption, and total porosity (TP) was calculated from OP and CP values. Characterization results were used to calculate statistically significant and valid regression equations, relating those properties with the raw material contents in the unfired mixture. For the particular raw materials and processing conditions used, the models clearly show how quartz contributes to increasing OP and the crucial role played by feldspar when CP and TP are to be minimized (circa 3 vol.%), and how the clay content can counteract that effect and lead to maximum closed porosity (∼14 vol.%).     

Properties and Applications of Morinda citrifolia (Noni): A Review

Morinda citrifolia commonly known as noni is a perennial plant originating in Southeast Asia, consumed over 2000 years. Due to its versatility of adaptation and use of the structures of the plant for different therapeutic purposes, noni attracted the attention of researchers from the pharmaceutical and food industry. Chemical and nutritional analyzes already performed in M. citrifolia reveal the existence of more than 200 phytochemical substances with bioactive properties such as acids, alcohols, phenols, saccharides, anthraquinones, carotenoids, esters, triterpenoids, flavonoids, glycosides, lactones, iridoids, ketones, lactones, lignans, nucleosides, triterpenides, sterols, and aromatic compounds. The high nutritional value of M. citrifolia may induce therapeutic effects, including antimicrobial and antioxidant properties. The main industrial products from this plant are beverages (juice drinks), powders (from dried fruits), oil (from seeds), and leaf powders. Biological and phytotherapeutic applications of M. citrifolia are promising, but more extensive studies are still required. Thus, this review aims to gather updated and comprehensive information on Morinda citrifolia, discussing its traditional use, biochemical, phytotherapics, and toxicological properties, as well as the recent advances in the processing and standardization of products derived from noni fruit.     

Tape casting of polysiloxane-derived ceramic with controlled porosity and surface properties

Tape casting has been applied to produce porous hybrid and SiOC ceramic tapes using ceramic precursors and commercially available polysiloxanes as polymeric binders. SiC particles of two different mean sizes (4.5 or 6.5?μm) were used as inert fillers to prevent shrinkage and increase mechanical stability. Macroporosity was adjusted by varying the azodicarbonamide (ADA) content from 0 to 30?wt.%. Decomposition of the polysiloxanes at 600?°C resulted in the generation of micropores with high specific surface area (187–267 m²?g^?1) and a predominant hydrophobic behavior. At 1000?°C mainly meso/macroporosity were observed (SSA: 32–162 m²?g^?1) accompanied by increased hydrophilicity. The influence of ADA content, SiC size, and pyrolysis temperature on open porosity (2.5–37%), average pore size (<0.01–1.76?μm), surface characteristics, and flexural strength (10.5–121?MPa) were investigated. The porous tapes with different surface characteristics and controlled structure are highly promising for applications involving membrane processes, particularly microfiltration systems (0.1–10?μm).     

Using granite rejects to aid densification and improve mechanical properties of alumina bodies

The industrial use of waste materials in the ceramic industry has been widely investigated. This work describes the research carried out on the manufacturing of alumina bodies with granite reject additions. The reject was used as produced by a local industry that saws granite stones into blocks and slabs. This industrial process produces a significant amount of that reject, which is discarded in sedimentation lagoons, landfill areas or simply thrown in rivers, resulting in environmental pollution. Alumina and the granite reject were ball-mill mixed with 5 wt% manganese oxide and pressed under an uniaxial load of 20 MPa. Samples were subjected to thermal analysis (DTA, TG and dilatometry) and sintered in air at 1300 and 1350^∘C during 1 h in an electric furnace. Sintered specimens were characterized by X-ray diffraction, apparent density, open porosity and flexural strength. The results showed that the addition of granite reject and manganese oxide enables low temperature sintering and remarkably improves (~300%) the cold mechanical properties of the alumina body.