Ubaldo Ortiz

Chemical structure and compatibility of polyamide–chitin and chitosan blends

This work presents a comparative study of the compatibilization of four binary blends with slight differences in their chemical structures. The natural polymers chitin (QA) and chitosan (QN) are blended with polyamide 6 (PA6) and polyamide 66 (PA66). The results, obtained using differential scanning calorimetry, infrared spectroscopy, and light and scanning electron microscopy, gave the following compatibilization sequence: PA6/QN ≈ PA66/QN > PA6/QA > PA66/QA. This behavior could be related to the ability of QN to form hydrogen bonds and also to the capability of the packing of PA66.

The reliability of thermocouples in microwave ceramics processing.

It is not rare to hear arguments against the use of thermocouples for taking temperatures in processes that are taking place under microwave fields. However, the simplicity of this device makes it attractive to consider its use. One question that arises when thermocouples are employed is whether the electric field perturbs the measurement, and if the thermocouple affects the processing. The process that was chosen for conducting this test was the synthesis of spinel (MgAl2O4) using microwaves as a power supply and hematite (Fe2O3) as an additive for both spinel formation promotion and susceptor. The alumina-based systems are very important to study because this is one of the most common ingredients in refractory materials. There are many discussions about the improvement of the process when microwaves are used, but a kinetic comparison cannot be performed if the temperature is unknown, and that is the reason for emphasizing the measurement techniques. The analysis of the obtained samples was carried out by X-ray diffraction of powders. The results of this work show that there is no difference between the products obtained when the thermocouple was inserted in the system, compared to processing without it; hence the thermocouple is appropriate for this application.

Production of MgO in an electric arc furnace: thermal analysis

The computer simulation presented here is the response to an industrial challenge about how the electric arc furnace, where the smelting process of magnesium oxide (MgO) takes place, should be charged to avoid shell overheating. If solid MgO is charged at a very high rate, the processing time becomes very long; on the other hand, if the feed rate is too slow, the external shell made of steel reaches temperatures above its melting point. Thus, it is necessary to reduce the electrode current or to charge more material to avoid shell overheating. With the aid of this model, a charge scheme for the furnace is proposed, having maximum production without shell overheating. Validation of the model has been carried out with temperature measurements along the external shell while the process was being conducted; the size and shape of the smelted zone after fusion were also compared with information obtained from the graphic results predicted by the model. Results from the model are in good agreement with the measurements. Calculation of the specific energy consumption can be provided with the input energy rate and the mass of the smelted MgO.

Characterization of SiC produced by microwaves

The purpose of this work is to present the characterization of silicon carbide that was produced in our laboratory by means of microwaves as an energy source, discussing process parameters such as power and achieved temperature. This material was processed from a silicon oxide and graphite mixture that was placed into an aluminum oxide crucible. The set was in turn placed into a multimode cavity in a location chosen according to the best heating rate. The power source was a magnetron operating at 2.45 GHz and at output power up to 2000 W for times as long as 1500 seconds. The mixture reached temperatures in the order of 2000°C, which is high enough for having an appreciable reaction degree. The lattice was determined by means of X-rays diffraction and the structure was observed by means of scanning electron microscopy. Most of the product was β-SiC, which was expected because the temperature was close to this polytype growth regime. One aspect that is pointed out is regarding with the variation of the structure related to the heating rate, despite the homogeneity of the lattice of the formed product, the exhibited structure went from coarse grains to whiskers needle shaped. Finally a comparison against SiC from an electrical resistance and commercial SiC for fired products is shown.

Polyamide/Biopolymer Blends

Abstract We prepared blends of polyamide 66 (P66) and chitin (QA) and its derivative, chitosan (AN), via the solution-casting technique. For P66 with 60% QN content, differential scanning calorimeter analysis showed an 81% decrease in the heat of fusion. When 15% P66 was added, the infrared spectral band of the carbonyl functional groups of the non-deacetylated portion of QN showed about 6 cm-1 displacement from its normal position. In addition, the carbonyl band of the P66 amide was expanded and displaced to the higher wavenumbers when QN was added. This spectral modification could be attributed to intermolecular hydrogen bonding between components, and the expansion of the P66 band could indicate an increase in disorder in the functional groups, namely, a transformation of P66 from the crystalline to the amorphous state. For P66/QA blends, no displacement of the functional group bands was detected, indicating the probable absence of miscibility of these blends. The morphology of the blends after solvent evaporation at 30°C was analyzed, using a cross-polarized optical microscope and a scanning electron microscope.

Synthesis and Study of Nanostructures Via Microwave Heating

This work is devoted to microwave heating of graphite, sucrose, calcined sucrose, and a mixture of graphite with sucrose to produce carbon nanotubes (CNTs). The samples were submitted to microwave radiation (power 800W, frequency 2.45 GHz) in air and high vacuum (10 −5 Torr) for 30 – 60 min. The oven temperature was approximately 1200°C. After vaporization the condensed material was collected on various fused silica targets (different morphologies were used). The samples were found to contain a significant proportion of nanotubes, nanoparticles and fibers (1-2.8 micrometers), which appeared to be highly graphitized and helical structured. After deposition, the morphology of carbon nanotubes was studied with SEM, TEM and AFM techniques. It was observed that multi-walled nanotubes (MWNTs) were produced by this method. The morphology of fused silicon based substrates (SiO 2 , SiC) was studied as an important factor for the growth of carbon nanotubes. Many aspects as the size and shape of the obtained nanotubes on different substrates (porous and non-porous fused silicon substrates) were achieved, as well as the concentration of them across the substrate and other properties.

Self-Affinity Analysis of the Fracture Surfaces of Polypropylene and Opal Glass.

In this work we report the self-affinity analysis of the fracture surfaces of a polymeric semicrystalline material and an opal glass. In the case of the plastic material, samples of isotactic polypropylene (i-PP) were prepared by varying the cooling rate from the melt; this resulted in different spherulite sizes. Samples were then broken in bend test after being immersed in liquid nitrogen. In the case of the opal glass, samples with different sizes of the opacifying particles, obtained by different thermal treatments, were broken in a punch test. In both cases the fracture surfaces were analyzed by both Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) in the contact mode. Self-affinity analysis was performed by the variable bandwidth method, covering a range of length scales spanning from a few nanometers up to ten micrometers. The roughness exponents are found to be of similar values close to ζ = 0.8 with the correlation length corresponding to the size of the spherulites in the plastic material and to the size of the opacifying particles in the opal glass. These results should be taken into account in the development of multiscale models and simulations of the fracture process of real heterogeneous materials.

Effect of Fe on Sintering of Al 2 O 3 -MgO-Fe 2 O 3 Spinel

The influence of Fe on the microstructure of Al 2 O 3 -MgO-Fe 2 O 3 spinel is described in this work. Heating a mixture of initial oxides in an electric furnace at 1400°C for 15 hrs produced the spinel. A ternary diagram for concentration ranges: Al 2 O 3 (5-75 mol%), MgO (10-80 mol%), and Fe 2 O 3 (3-70 mol%) summarize the constitution of this spinel. Amount, composition and weight ratios of each phase were determined by X-rays powder diffraction. Microstructure of specimens was characterized by scanning electronic microscopy and Xray spectrometry. Distribution, size, shape of phases and pores were examined. Hardness measurements of spinel completed this study.

Development of iron layers on the internal wall of reduction reactors

Abstract Refractory bricks are the most common materials used in equipments for carrying processes at high temperatures, such as the production of steel, cement and glass. These bricks are exposed to severe operation conditions, their life determines if an equipment should be stopped for reparation or replacement of the bricks. One of the phenomena that is present inside reactors or furnaces with an internal wall covered by refractory material is the formation of layers. As they growth, they cause disturbs in the product flow or at least decreases the reactor or furnace capacity, and in the worst case it is necessary to stop the equipment for major reparations. This work is centred in the formation of layers inside the direct reduction reactors. These layers are formed over the firebrick (Al 2 O 3 , SiO 2 ) wall from the Direct Reduced Iron (DRI) that is being processed in the reactor. The aim of this work is to describe the mechanism of formation and growth of these layers. We conducted several test for simulating the formation of layers by the application of shear stresses at high temperatures and under a reductive atmosphere to the a DRI pellet-refractory interphase. The amount of DRI adhered to the sample bricks was measured following an experimental design of nine independent variables. Temperature, shear stress and time were identified as important variables for the mechanism of formation and growth of the layers. Confirmation of the importance of these variables was determined by means of a proposal for avoiding the adhesion problem. This proposal consists in a treatment on the surface of the brick that minimizes the adhesion of DRI. The successful treatment of more than 6000 bricks for operating plants proves that our conclusions are correct. ©.