Acid Digestion Tests Research Articles

The effect of depth-dependent carbonation on the interfacial strength between GFRP reinforcement bar and reactive magnesia cementitious composites

Reactive magnesia cement (RMC) is an emerging class of low-alkaline and CO2-sequestering binder, which can mitigate the deterioration of GFRP reinforcements induced by a high-alkaline environment, e.g., in Portland cement. This study investigated the slip behavior of GFRP rebar embedded in RMC composite, which varies with carbonation depth significantly. The variation of the interfacial bond was determined by a specially designed push-out test of the GFRP core; the variation of the carbonation degree and microstructure was examined by SEM-EDX, MIP, XRD, TGA, FTIR, and acid digestion tests. Both properties demonstrated a similar trend, decreasing rapidly with increasing depth. A new finite element model that considers the depth-dependency of the matrix compositions and the rebar-to-matrix interfacial bond is established. It can predict the constitutive bond-slip behavior of a long GFRP rebar embedded in an RMC composite with non-uniform carbonation.

Void Content Determination of Carbon Fiber Reinforced Polymers: A Comparison between Destructive and Non-Destructive Methods.

The properties of composite materials are highly dependent on the fiber and matrix fraction and on the porosity resulting from micro voids. This paper addresses void content characterization and the constituent content of composite materials by resorting to a comparison of destructive and non-destructive methods. The work presents the detailed procedures of two destructive methods, using acid digestion of epoxy resins matrices, and compares their processes. It also presents the results of a non-destructive method, by means of Micro Computed Tomography (MicroCT). The results of both destructive and non-destructive methods are compared, and a recommendation is made based on the application and the type of composite being analyzed. The MicroCT showed better and more consistent results in detecting voids in the material, while the acid digestion tests provided better results about the fiber and matrix percentage. Exported results from the MicroCT scanning with actual locations of voids were used in numerical analysis, to examine the feasibility of using them, whether by developing models that map damage in the proximity of the void, or by developing models that predict the properties of the entire material with respect to the content, shape, and distribution in the material.

Efficacy of Enzymatically Induced Calcium Carbonate Precipitation in the Retention of Heavy Metal Ions

This study evaluated the efficacy of enzyme induced calcite precipitation (EICP) in restricting the mobility of heavy metals in soils. EICP is an environmentally friendly method that has wide ranging applications in the sustainable development of civil infrastructure. The study examined the desorption of three heavy metals from treated and untreated soils using ethylene diamine tetra-acetic acid (EDTA) and citric acid (C6H8O7) extractants under harsh conditions. Two natural soils spiked with cadmium (Cd), nickel (Ni), and lead (Pb) were studied in this research. The soils were treated with three types of enzyme solutions (ESs) to achieve EICP. A combination of urea of one molarity (M), 0.67 M calcium chloride, and urease enzyme (3 g/L) was mixed in deionized (DI) water to prepare enzyme solution 1 (ES1); non-fat milk powder (4 g/L) was added to ES1 to prepare enzyme solution 2 (ES2); and 0.37 M urea, 0.25 M calcium chloride, 0.85 g/L urease enzyme, and 4 g/L non-fat milk powder were mixed in DI water to prepare enzyme solution 3 (ES3). Ni, Cd, and Pb were added with load ratios of 50 and 100 mg/kg to both untreated and treated soils to study the effect of EICP on desorption rates of the heavy metals from soil. Desorption studies were performed after a curing period of 40 days. The curing period started after the soil samples were spiked with heavy metals. Soils treated with ESs were spiked with heavy metals after a curing period of 21 days and then further cured for 40 days. The amount of CaCO3 precipitated in the soil by the ESs was quantified using a gravimetric acid digestion test, which related the desorption of heavy metals to the amount of precipitated CaCO3. The order of desorption was as follows: Cd > Ni > Pb. It was observed that the average maximum removal efficiency of the untreated soil samples (irrespective of the load ratio and contaminants) was approximately 48% when extracted by EDTA and 46% when extracted by citric acid. The soil samples treated with ES2 exhibited average maximum removal efficiencies of 19% and 10% when extracted by EDTA and citric acid, respectively. It was observed that ES2 precipitated a maximum amount of calcium carbonate (CaCO3) when compared to ES1 and ES3 and retained the maximum amount of heavy metals in the soil by forming a CaCO3 shield on the heavy metals, thus decreasing their mobility. An approximate improvement of 30% in the retention of heavy metal ions was observed in soils treated with ESs when compared to untreated soil samples. Therefore, the study suggests that ESs can be an effective alternative in the remediation of soils contaminated with heavy metal ions.

Seasonal assessment of surface water for selected traces in the vicinity of a thermal power plant

The present study has been conducted to evaluate the role of seasonal variation on the heavy metals pollution levels in the surface water bodies located in the environs of a thermal power plant in Bhilai, central India. Acid digestion test on fly ash sample was conducted for the total concentrations of traces (Cr, Cu, Fe, Mn, Pb, and Zn) and, a laboratory batch leaching test to assess the mobility of the selected metals. The average leached percentage order of metals from fly ash are—Cr > Pb > M>Zn > Cd > Fe > Cu was observed. Pre-monsoon metal concentrations ranged between 0.3 to 3.298 mg/L for Cr, 0 to 0.33 mg/L for Cu, 0.37 to 3.51 mg/L for Fe, 0.15 to 0.26 mg/L for Pb, 0.057 to 2.931 mg/L for Mn, and 0.01 to 0.397 mg/L for Zn. Whereas, for the post-monsoon, it ranged between 1.45 to 2.316 mg/L for Cr, 0.007 to 0.009 mg/L for Cu, 0 to 0.731 mg/L for Fe, 0.07 to 0.12 mg/L for Pb, 0.046 to 1.272 mg/L for Mn, and 0.108 to 0.341 mg/L for Zn. These outcomes, regarding the possible level of contamination in water sources, are a major issue with seasonal variation, as it may influence the metal mobility.

A new sample preparation method for crude or fuel oils by mineralization utilizing single reaction chamber microwave for broader multi-element analysis by ICP techniques

The objective of this study was to develop an effective and routine single sample preparation method to accurately and precisely analyze multiple elements (up to 57) in crude oils using both an inductively coupled plasma-optical emission spectrometer (ICP-OES) for high abundance elements and a triple quadrupole-inductively coupled plasma-mass spectrometer (QQQ-ICP-MS) (or ICP-MS) for low abundance trace and ultra-trace elements. A critical aspect of this study was to develop a single sample preparation method that could be effective in analyzing the largest number of quantifiable elements with instruments used in tandem to cover a wider and more practical combined dynamic range. Three sample preparation techniques were investigated and tested, including high pressure combustion with strong-acid digestion, high pressure and high temperature strong-acid digestion within Parr bombs, and high temperature and high pressure digestions in a Single Reaction Chamber (SRC) microwave. For the combustion method, no element showed recovery above 75%, thus this method was deemed unacceptable for accurate and precise analysis of crude oil. Average recoveries ranging from 94% to 106% for 19 analytes were achieved with high pressure and high temperature acid digestion within Parr bombs. A drawback of the method, however, was a rather small sample sizes (100mg) that could be achieved without venting, which places limitations on detection and quantitation limits of large numbers of low abundance analytes in natural crude oils. The best of the SRC microwave-assisted acid digestion tests, however, was also shown to be acceptable for 19 analytes using a certified organometallic standard, with average recoveries ranging from 93% to 113%. Because of rapid sample throughput and the larger sample sizes (1.2g sample size per digestion session) that can be accommodated with the single reaction chamber microwave digestion technique, better method detection and quantification limits and high precision on a range of low abundance elements could be achieved. We also then successfully tested the recovery of 53 elements with this SRC microwave method by adding a multi-element spike to Conostan base oil. This optimum SRC digestion method tested was then used to examine a NIST natural crude oil research material (NIST RM 8505) in an attempt to quantify up to 57 elements. The mean vanadium concentration (mass fraction) is reported as 390±0.4µg/g, the mean value of 5 replicate digestions by our method, which agrees well with the recommended value for the only element recommended for NIST 8505 of 390±10µg/g. The number of quantified analytes for the RM 8505 was further extended to a total of 52 elements with RSDs <5% for 38 elements, between 5% and 10% for 10 elements, and between 10% and 15.6% for 4 elements, all of which met our acceptability limits set at ≤20% RSD. Of the 57 elements analyzed in RM 8505, certain elements B, Nb, and W, although above method quantitation limits, were judged unacceptable because RSDs were ≥31.4%, whereas Ag and Tl were below method quantitation limits, and their RSDs were ≥44.2% and judged unacceptable. However, these elements have been quantified in other natural crude oils with higher abundances, which indicates that up to 57 elements can be potentially assessed in crude oils or refined oils with this method. The NIST RM 8505 crude oil reported here and others are being evaluated as potential natural crude oil standards to provide references values for more routine multi-element analysis.

The use of response surface methodology (RSM) to optimize the acid digestion parameters in fiber volume fraction test of aircraft composite structures

An acid digestion test has been widely used to determine the fiber volume fraction, Vf and void content of the PMCs laminate. Three main testing parameters of volume of acid, digestion period, and temperature were found to influence the resin extraction during the test. The study was aimed to establish the optimum values of those testing parameters through the use of statistical method of RSM. The exact values of each parameters was evaluated based on Vf, and hence, the percentage of difference in comparison to the target value. The results have indicated that the proposed mathematical model could adequately describe the performance indicators within the limits of the factors investigated. As per described via the model relationship, the optimum condition were established as 30 ml of sulfuric acid and 3.5–4 h of digestion period at 175 ± 5 °C. The error between the predicted and actual experiment values were between −1.52 and −2.43%.

Short-term leaching study of heavy metals from LD slag of important steel industries in Eastern India

Considering Linz-Donawitz (LD) slag as a waste material for its bulk utilisation, there is a possibility that heavy metals will leach to environment. It necessitates the study on physical, chemical, mineralogical and heavy metals leaching characteristic of LD slag. Short-term leaching procedures like batch leach test (BLT), toxicity characteristic leaching procedure (TCLP), strong acid digestion test (SADT) and American Society for Testing and Materials (ASTM) shake test were carried out for assessing heavy metals leaching potentiality. As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Se, V and Zn were leached from LD slag from three major steel industries i.e. Roulkela, Bokaro and Tata Steel Plants of India and were analysed by inductively coupled plasma optical emission spectrometer (ICP-OES). Most of the heavy metals like Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn showed relatively lesser leachability. Toxic heavy metals like As, Cd, Se and V were not leached by BLT, TCLP as well as ASTM shake test and were below detection limit. Rourkela LD slag heavy metals leaching were relatively higher than Bokaro and Tata Steel Plant LD slag and were below permissible limit. The present study reflects about non-hazardous nature of LD slag.

Individualisation of the Biological Remains from Anthropological Perspective-A Case Study

A teenage boy went to see a wrestling bout in nearby village and disappeared mysteriously. On presumption of death under suspicious circumstances, the parents lodged a complaint and a murder case was registered in police station under section 302, 34 IPC. The incidence caused lot of unrest and protesting villagers blocked roads. After about two weeks, the skeletal remains of a human body were found on the bank of Pong Dam Lake in Himachal Pradesh. The police visited the spot and collected the skeletal remains for post-mortem examination. After about two weeks of death, a team of forensic experts from RFSL, Dharamshala visited and scientifically examined the spot and skeletal remains kept in the mortuary, collected and photographed the clue materials/physical evidences. The skeletal remains were found nibbled by wild animals indicating that the body got exposed after water level at the dam receded. The wild animals attacked and nibbled the remains and gnawing marks were seen on bones, metatarsal and heel region. In the present case, diatom analysis, study of skeletal remains, hair and faecal matter examination and DNA fingerprinting was done to ascertain the real cause of death, age, sex and identity of the person. For establishing identity and estimating the age and sex from the skeletal remains, forensic experts examined the skull, mandible and maxilla for dental eruption, pelvis and long bones on the basis of osteological, anthroposcopic, morphological and anatomical examination/assessment and the remains were found to be of Homo sapiens (Human) which were morphologically and anatomically consistent with male individual under 18 years of age. For examining the drowning case, water sample, in which possible drowning took place and femur bone sample was used for detection of diatoms. Acid digestion test was used and a correlation was established between diatoms detected in water and bone sample indicated ante-mortem drowning. In DNA fingerprinting blood samples of the parents matched with the DNA extracted from the bones which proved identity. After morphological and microscopic examinations the black hair embedded in the soil and brown hair with animal droppings collected from the spot revealed that black hair were human head hair and animal dropping was a mixture of human and animal hair probing that some wild animal have eaten the body and passed the droppings.

Void Content Determination of Fiber Reinforced Polymers by Acid Digestion Method

Porosity of the fiber-reinforced polymer (FRP) is one of very important quality characteristics for the advanced use of the material in order to ensure full performance properties are attained. It was found that the porosity values of FRP in typical aircraft composite parts must be lower than 2.5 % to achieve the required mechanical properties. The most common method for measuring the void content is through acid digestion testing or burn-off method, since it provides the true values that could be used to generate the database properties of the materials. Thus, this paper discussed the detail of the acid digestion test procedures for the void content measurement of FRP, especially with regards to the suitable testing time and chemical volumetric quantity required to ensure the matrix of test sample has been completely extracted. In order to attain this, different test samples for different processing techniques were prepared. Subsequently, the findings were discussed within the context of void content in cured monolithic composite for different types of process, in which the samples from the VBO-oven curing process were compared with those of the autoclave-cured samples. In the VBO-oven curing process, the use of an intensifier during the curing provided higher void content of 15.52% in comparison with those achieved through the debulking process (10.91%). It has been clearly observed that the debulking produced a substantial effect towards the air evacuation mechanism within the laminate.

Properties of Pultruded Jute Fiber Reinforced Unsaturated Polyester Composites

This paper deals with an experimental study on the properties of pultruded jute fiber reinforced unsaturated polyester composite (PJFRC). The ratio of fiber to matrix is approximately 70:30 by volume. Compression and flexural testing were performed in order to study the mechanical properties while TMA and DMTA were used to study the thermal properties of the composites. Morphological aspects of the composites were also evaluated using an optical and scanning electron microscope. Compression and flexural stress–strain curves showed a linear portion at initial loading phase followed by yield and plastic deformation. For the DMTA evaluation it was found that the storage modulus is strongly dependent on temperature and degrades with increasing temperature. The TMA result showed a contraction of composite upon heating instead of expansion. The acid digestion test result confirmed that the fiber content was approximately 70% by volume.

Non-Destructive Evaluation of Carbon Fiber Composite Reinforcement Content

The use of light-weight, high-strength composite materials in motors, generators, and energy storage devices has become common as a means to maximize energy density. To ensure reliability, non-destructive and destructive evaluation techniques have been employed to measure the mechanical properties of fabricated components. In carbon fiber-reinforced, polymer matrix composites, mechanical strength is primarily derived from the fiber volume fraction. Due to the lack of a nondestructive method, common techniques for fiber volume determination are currently destructive. In this investigation, a non-destructive method for the measurement of the fiber volume fraction of carbon fiber-reinforced, polymer matrix composites has been developed using cold neutron prompt gamma activation analysis (PGAA). Fiber volume determination is accomplished in this technique by measuring and comparing the carbon and hydrogen content in a given sample (or samples). PGAA is a nuclear analytical technique performed by exposing a sample to neutron radiation. PGAA measurements are non-destructive and can be performed without chemical preparation of the sample. Fiber volumes of several composite coupons have been determined relative to standard samples of known fiber volume and measurements are in good agreement with values predicted by acid digestion tests. Fiber volume measurement using PGAA can potentially be applied to any composite material where the contents of the matrix and reinforcement differ. The technique can also be spatially sensitive, with resolution limited by the dimensions of the neutron beam that is used.

Lamb wave assessment of fiber volume fraction in composites.

Among the various techniques available, ultrasonic Lamb waves offer a convenient method of examining composite materials. Since the Lamb wave velocity depends on the elastic properties of a material, an effective tool exists to evaluate composites by measuring the velocity of these waves. Lamb waves can propagate over long distances and are sensitive to the desired in-plane elastic properties of the material. This paper discusses a study in which Lamb waves were used to examine fiber volume fraction variations of approximately 0.40-0.70 in composites. The Lamb wave measurements were compared to fiber volume fractions obtained from acid digestion tests. Additionally, a model to predict the fiber volume fraction from Lamb wave velocity values was evaluated.

Fractal assessment of finely ground limestone for flue gas desulphurisation

Industrial minerals, those utilised for their physical properties and chemical content, e.g., limestone, often employ comminution during their preparation. A study was performed to investigate if the type of pulveriser used to comminute limestone, a grade suitable for flue gas desulphurisation, influenced its morphology and subsequent behaviour. Samples of the limestone were pulverised by three different devices a hammer mill, rolls crusher and ball mill. A narrow size fraction was removed from each of the products by elutriation. These fractions were then subjected to sulphuric acid digestion tests, to simulate the desulphurisation process. The tests revealed that the amount of acid consumed, i.e., limestone utilisation, varied with the pulverisers under study, with the hammer mill having the highest limestone utilisation. From SEM micrographs of the limestone fragments their overall geometric shape and fractal dimension were determined, using image analysis procedures. The fractal dimension is a useful descriptive parameter for characterising boundaries that take on a randomly rugged appearance. Using the classical geometric shape factors, aspect ratio and circularity, one could not distinguish between the three comminution products. However, fractal analysis was sensitive enough to differentiate between the fragments produced by the different pulverisers. Hammer milling produced the most rugged particles followed by rolls crushing and ball milling respectively.

Determination of Fiber Volume Fractions by Optical Numeric Volume Fraction Analysis

A method for determining the fiber volume fraction in continuous fiber composites by automatically counting the fiber ends per unit area in digitized microscope images of representative cross sections has been developed. Since fiber counts are digital variables, the accuracy of the method is essentially independent of small variations in microscope focus and specimen surface preparation. In addition to producing averaged data, the method enables the construction of volume fraction variation profiles ranging from the finest possible scales up to full size components. Results are in agreement with values obtained by acid digestion tests.