Materials Science Forum Vols. 727-728

Abstract: The growing concern with environmental issues in tanneries and the search for a technological solution to their wastes are evaluated in this study. The waste named leather shaving was chemically treated aiming the immobilization of the chromium ion in a Portland cement paste, using mortars. 28 days-aged samples were evaluated in relation to their physical properties and axial compressive strength. Results showed that the alternatives used for the pretreatment were effective for the dissolution of the material, but they impaired the mechanical strength of samples.

Abstract: The red mud (RM) is a solid waste derived from the processing of bauxite ore to produce alumina and it is considered a hazardous waste due to its high pH. This paper describes the use of mud untreated and after calcination at distinct temperatures (450, 650, and 1000°C) attempting to improve its reactivity. The Portland cement was replaced up to 30 wt% red mud, and its addition changed the hydration process, evaluated by calorimetric studies of early hydration and setting time. By comparing with the reference mixture (without red mud), the obtained results confirm the potential of the red mud to be used as pozzolanic additive to cementitious materials. Temperature of hydration was monitored by a quasi-adiabatic calorimeter (Langavant). The hydration temperature increases with RM addition, particularly if calcined in the same interval (450-650°C). In this condition, the hydration process is accelerated.

Abstract: Brazil is one of the main producers of dimension stones in the world and most of its production is for international market. Cutting granites and marble blocks to produce plates, and polishing theses plates, generate a fine waste whose characteristics indicate possibilities to be used in other products, such as ceramic material. The residue, also known as abrasive slurry, can cause environmental damage depending on chemical composition. The proper treatment, storage and application of this material ask for studies about their composition and transformations along time. The aim of this work is to analyze five deposits of dimension stone wastes with different ages and stored under different conditions. Residues have high compositional variability, but none showed elements content that could be considered dangerous to the environment.

Abstract: Clay minerals, principally montmorillonites, offer a wide range of applications as adsorbent materials [1]. Clay layers in barriers may impede migration of toxic substances to the environment, in which case the effect of organic compounds on the particle-particle interaction and the mechanical stability of clay barriers must be considered [2]. The stability of band-like networks formed by partial overlapping of silicate layers and interlayer is affected by molecules and ions which are adsorbed on the external surfaces [3]. The evaluation of adsorbent materials effects can be done through viscosity measurements, in the present work some viscosity tests were done.

Abstract: The construction industry in addition to being considered one of the biggest natural resources consumers is still responsible for generating large quantities of residues. The impacts caused by these residues have motivated research aimed at developing new techniques for reuse and recycling this material by using as raw material to make alternative materials. The introduction of demolition residues (DR) in soil-lime bricks replacing part of the pozzolan becomes possible due to the cementing properties that these residues may present when finely grounded. This study aims to evaluate the durability of soil-lime blocks embedded with demolition residues. For this study the raw materials were characterized by particle size distribution analysis, X-ray diffraction and chemical analysis. Then test specimens were prepared using mixes in a 1:10 ratio of lime:soil and embedded with residue in partial replacement of lime, in the proportions of 25%, 50% and 75% with curing period of 90 days. Later, the test specimens were evaluated for durability. The results showed that soil-lime bricks embedded with contents above 50% of residues had their durability affected.

Abstract: Silicon carbide (SiC) has been employed in many different fields such as ballistic armor, thermal coating, high performance mirror substrate, semiconductors devices, among other things. Plasma application over the silicon carbide ceramics is relatively recent and it is able to promote relevant superficial modifications. Plasma expander was used in this work which was supplied by nitrogen and switched by a capacitor bank. Nitrogen plasma was applied over ceramic samples for 20 minutes, in a total medium of 1440 plasma pulses. SiC ceramics were produced by uniaxial pressing method (40 MPa) associated to isostatic pressing (300 MPa) and sintered at 1950°C under argon gas atmosphere. Silicon carbide (β-SiC - BF-12) supplied by HC-Starck and sintering additive (7.6% YAG - Yttrium Aluminum Garnet) were used in order to obtain the ceramics. Before and after the plasma application, the samples were characterized by SEM, AFM, contact angle and surface energy measurement.

Abstract: Silicon Nitride is largely used as the base material to manufacture cutting tools. Due to its low thermal expansion coefficient it is ideal candidate for CVD diamond deposition. In this work, we functionalized the surface of silicon nitride inserts (Si₃N₄) with a polymer (PDDA Poly (diallyldimethylamonium chloride - Mw 40000)) to promote seeding with nanodiamond particles. The seeding was performed in water slurry containing 4 nm diamond particles dispersed by PSS Poly (sodium4-styrenesulfonate) polymer. CVD diamond films, with high nucleation density, were deposited in a hot filament reactor. Film morphology was characterized by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Diamond film quality was determined by Raman Spectroscopy. CVD diamond film adherence was evaluated using Rockwell C indentation.

Abstract: Clay blends are products used in several industrial sectors, such as petrochemical or pharmaceutical. In this work we describe a natural clay blend occurring in northeastern Brazil. The aim was to purify and investigate their rheological and physical-chemical properties. Foster essays with water and organic solvents were utilized to access the swelling properties of the analyzed sample. Powder X-ray diffractograms (PXRD) were utilized to analyze qualitatively the clay minerals presents in the sample blend. Scanning eletronic microscopy (SEM) and Malvern techniques were used to investigate the sample clay morphology. The purification proceeding allowed separate distinct clay phases with different colors. PXRD analysis demonstrated that each clay phase presents similar structure. SEM and Malvern analysis showed distinct morphology and different size distribution for each clay phase. Our results revealed that the analyzed sample clay may be classified as smectite blend with strong potential for use in pharmaceutical and cosmetic products.

Abstract: The main deposits of bentonite clays are located in the district of Boa Vista, in the State of Paraiba, Brazil. The random exploration of these deposits for many years is causing the clays to be depleted, and this will turn into a serious problem to the national petroleum industry. So, this work aims to study the characterization of new deposits of bentonite clays in the district of Cubati, in the State of Paraiba, Brazil, with the objective of developing purified organoclays, using a hydrocyclone, from ionic and non-ionic surfactants for use in drilling fluids. The characterization of the studied clay samples was done by applying the following techniques: granulometric analysis by laser diffraction (GA), X-ray diffraction (XRD) and chemical analysis by X-ray fluorescence (EDX) and thermogravimetric (TGA) and differential thermogravimetric (DTA) analysis. The characterization is typical of bentonites and the dispersions present rheological properties which meet Petrobras’ specifications for diesel oil media, organofilized with Praepagen WB.

Abstract: Organically modified clay minerals are widely used as sorbents for hydrophobic organic compounds e.g., organic pollutants treatment from water solutions. Natural clay materials are hydrophilic and therefore they are not efficient sorbents for organic compounds. Intercalations of natural clay materials, with organic cations, with quaternary ammonium groups may become these clays hydrophobic. Vermiculite is the mineralogical name given to hydrated laminar magnesium-aluminum-iron silicate; this natural clay was modified and used for the production of organically modified clay (organovermiculite), with the purpose of its use in removing organic contaminants. The organovermiculite was prepared using different concentrations of distearyl dimethyl ammonium chloride (praepagen) based on cationic exchange capacity of the clay. It was evident from the X-ray diffraction that the salt was incorporated to the clay structure confirming its organophilization and through the Foster swelling test it was observed the affinity between the organic pollutants and the organovermiculite.