Paste Composition Research Articles

Power ultrasound-assisted enhancement of granulated blast furnace slag reactivity in cement paste

The impact of the power ultrasound (PUS)-assisted preparation technique on the physicochemical and mechanical characteristics of cement-granulated blast furnace slag (GBFS) pastes was studied. Pastes containing GFBS with varying particle size fractions, partially replacing Portland cement, were tested using PUS in pulse mode in a sonoreactor with closed-circuit cooling. The best-performing cement-GBFS composite paste showed a notable increase in compressive and flexural 2-day strengths (132% and 58%, respectively), as well as Vickers hardness and modulus of elasticity (98% and 74%, respectively) when compared to conventional mixing procedures. Similarly, the BET surface area increased by about 111%, cumulative heat release increased by about 34% after 2 days, reduced substitute setting times (initial by about 32%, final by about 55%), and portlandite content decreased by about 29%. The power of this association is linked to C-S-H/C-A-S-H nucleation seeding, which can be formed via an interfacial mediator induced by PUS.

Analysis of the Impact and Mechanism of Polyacrylate-Based Composite Paste on the Performance of Recycled Aggregate

This study developed three composite slurries for coating recycled aggregate by incorporating polyacrylate emulsion, fly ash, and gypsum into a cement-based mixture. The filling and pozzolanic effects of fly ash help to improve microcracks in the recycled aggregates. The polyacrylate emulsion forms a strong bonding layer between the cement matrix and the aggregates, enhancing the interfacial bond strength. Based on relevant studies, the following mix designs were developed: Slurry 1 consists of pure cement paste; Slurry 2 contains 15% fly ash and 3% gypsum added to the cement paste; Slurry 3 adds 22% polyacrylate emulsion to the slurry. The study first compared the effects of the three composite slurries on the crushing value and water absorption of recycled aggregates, and then analyzed their impact on the mechanical properties, permeability, and drying shrinkage of concrete. Finally, the mechanisms behind the enhancement were investigated using the Vickers Hardness Test (HV), Mercury Intrusion Porosimetry (MIP), and scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS). The results showed that the polyacrylate emulsion composite slurry had the most significant improvement effect. For recycled aggregate AL, the crushing value decreased from 28.8% to 22.5% and the saturated surface–dry water absorption decreased from 15.1% to 13.8% after cement slurry modification. After coating with the composite slurry, the crushing value further dropped to 18.2% and the water absorption to 9.5%. Two aspects of the performance of recycled aggregates are enhanced with the polymer composite slurry: first, fly ash provides nucleation sites for CH, reducing the tendency for directional CH alignment. Second, the long chains of PAE (polyacrylic ester) encapsulate cementitious particles, effectively filling surface defects on the recycled aggregates, improving the bonding strength at the new-to-old interface, and significantly enhancing the performance of both recycled aggregates and recycled concrete.

Stereolithography Printing and Mechanical Properties of Polyethylene Glycol Diacrylate/Hexagonal Boron Nitride Ceramic Composites

To enhance the mechanical properties of bioceramic composite bone scaffolds, a composite paste of polyethylene glycol diacrylate (PEGDA) and hexagonal boron nitride (h‐BN) with a solid content of up to 42 wt% was developed in this study. The part was produced using stereolithography (SLA). The SLA printing parameters and material ratios of the paste were optimized through a homogeneous design and mechanical property tests. The results indicate that the single‐line curing width of the PEGDA/h‐BN paste in the XY plane ranged from 172 to 209 μm, while the curing depth of a single layer along the Z‐axis ranged from 99 to 154 μm. Laser power was identified as the primary factor influencing both the width and depth of curing. The compressive strength of the printed sample of PEGDA/h‐BN ceramic composite paste was measured at 222.4 ± 5.6 MPa, which is 61 times greater than the compressive strength of a pure PEGDA structure and comparable to that of cortical bone (100‐230 MPa). Finally, the superior biocompatibility of PEGDA/h‐BN ceramics was confirmed through cytotoxicity experiments. Consequently, PEGDA/h‐BN ceramic composites meet the mechanical properties and biocompatibility requirements necessary for bone tissue applications, indicating promising potential in the field of bone tissue engineering.

Electrochemical boost via thermally reduced graphene oxide for tailoring composite paste electrodes

Carbon-based composite materials are employed in diverse electrochemical applications, such as in catalysis, (bio)molecular sensing, and energy storage. In practice, electrode material needs to be highly conductive to allow high-speed electron transference to electrolyte species and possess high-surface area to obtain greater measured signals and power capabilities, as well as long useful life and stability. In this sense, graphene derivatives emerge as interesting candidates, even more so if they constitute part of practical, economical and versatile paste electrodes.This work presents a detailed analysis of the electrochemical performance of paste electrodes fabricated with multilayer partially reduced graphene oxide (rGO). The rGO was strategically produced via thermal treatment as a key factor that minimizes both mass loss and energy consumption. The results obtained through diffraction, microscopy and spectroscopy techniques show an effective partial reduction in the range of 100 to 400 °C. Furthermore, the enhanced electrochemical performance of rGO was determined by exploring the specific capacitance from cyclic voltammetry (CV) and galvanostatic charge–discharge measurements (GCD) as well as charge transfer resistance via electrochemical impedance spectroscopy (EIS). Our results evidence how an integral performance with suitable chemical, structural and morphological properties achieved for GO heat-treated at 200 °C leads to an improved electronic conductivity when a small part is combined with graphite in paste electrodes. This latter combination provides higher versatility compared to other alternatives since it arises as an economical and effective carbonaceous matrix for (bio)electrochemical sensors, hybrid supercapacitors or other desired nanotechnological applications.

The Concept of Using 3D Printing Technology in Ceramic Foundry Filter Manufacturing

AbstractThe article presents the concept of using 3D printing technology in ceramic foundry filter manufacturing. They are a crucial component for obtaining an acceptable quality of nickel superalloys by carrying out the process using the precision casting method. Commonly used filters of this type have a number of disadvantages. They are characterized by irregularity of the filtering structure, high brittleness, lack of resistance to mechanical shocks, and impacts of a stream of liquid metal. All these factors create a risk of introducing the material from the damaged filter into the casting mold, which translates into contamination of the casting alloy, and thus the occurrence of casting defects such as nonmetallic inclusions. The hope for a change in this state of affairs is the use of additive manufacturing technology in their production, which by assumption will allow to obtain a product with a repeatable shape, high mechanical resistance, and a specially designed structure regulating the flow of liquid metal into the mold during casting. The suitability of robocasting and binder jetting technology for producing filtration structures was initially assessed. The results have presented the selection of ceramic powder, as well as the development of the composition of the ceramic paste. The parameters of paste preparation and 3D printing individual processes were described. Moreover, the representative microstructures and basic mechanical properties of samples obtained by both of the compared technologies were presented. Furthermore, the final effect of prototype casting filters with a repeatable shape, manufactured with the use of both technologies, was presented, which were transferred for further technological research in a foundry producing critical aircraft engine parts. The possibilities of using each technology in various applications were also discussed.

Wear and roughness analysis of two highly filled flowable composites.

This in vitro study aimed to evaluate surface roughness and wear of highly filled flowables and traditional packable composites. Additionally, the effect of polymerization time on these parameters was evaluated. Two flowable higly filled composites (CMf-Clearfil Majesty ES flow-low viscosity, Kuraray and GUf-Gaenial Universal Injectable, GC) and two packable composites (CM-Clearfil Majesty ES-2, Kuraray and GU-Gaenial A'CHORD, GC) were used to create 160 specimens (n = 40;8 × 6×4mm). For each tested material, two subgroups were considered according to the polymerization time (n = 20): 10s or 80s. After setting, the specimens were subjected to chewing simulations (240.000 cycles, 20N), and wear was measured by the laser integrated in the chewing simulator. The surface roughness was measured using a rugosimeter, before and after chewing cycles. Two representative specimens per group were observed under scanning electron microscope (SEM). Data were collected and statistically analyzed (p < 0.05). Wear analysis highlighted statistically significant differences between the groups: CMf10-CMf80 (p = 0.000), CMf10-CM10 (p = 0.019), CMf10-GUf10 (p = 0.002), CM10-CM80 (p = 0.000), CM80-GUf80 (p = 0.02), GUf10-GUf80 (p = 0.000), GUf10-GU10 (p = 0.043) and GU10-GU80 (p = 0.013). Statistically significant differences in surface roughness were highlighted between the groups: CMf10-CMf80 (p = 0.038), CMf80-CM80 (p = 0.019), CMf80-GU80 (p = 0.010), CM80-GUf80 (p = 0.34) and GUf80-GU80 (p = 0.003). Surface roughness and wear of highly filled flowable composites were comparable to that of traditional paste composites. Furthermore, a longer curing time leads to an improvement in the mechanical properties of the composites. Highly filled flowables can be a valid alternative to paste composites in occlusal areas due to its similar surface roughness and wear values, especially when overcured.

Study of archaeological ceramics from the north coast of Peru by EDXRF and exploratory multivariate analysis

This article presents the first results for elemental composition of 193 fragments ceramic from four sites located in Ventarrón-Collud archaeological complex, Peru. The results from EDXRF and multivariate analysis indicated statistical similarity among four groups of ceramic fragments, selected by remarkable stylistic variation, collected from different archaeological space/time contexts. The correspondence in the elemental composition of the ceramic paste of the artifacts corroborates the hypothesis that similar raw materials were used consistently throughout the entire occupation of this archaeological complex.

Improved thermal shock reliability of Ag paste sintered joint by adjusted coefficient of thermal expansion with Ag-Si atomized particles addition

In this study, two kinds of atomized Ag-20 wt%Si and Ag-50 wt%Si particles are fabricated and added to Ag paste to fabricate composite pastes to achieve a low coefficient of thermal expansion (CTE), and their performance stability in SiC power module is evaluated under thermal shock from −50 to 250 °C. Four kinds of composite Ag pastes using the two kinds of atomized Ag-Si addition with 10 % and 30 % were obtained, AS20-10, AS50-10, AS20-30 and AS50-30, respectively. The results show that the CTE reduction intensifies with increasing Ag-Si atomized particle content. The retention ratio of shear strength of AS20-30 sintered joint after 1000 cycles was 102.3 %, which means the shear strength did not decrease during so harsh thermal shock test. The mechanism was discussed in detail. In addition, the properties such as thermal conductivity and electrical conductivity for the composite pastes were also evaluated to gain a more comprehensive understanding for the new materials especially for the design of SiC power modules with a long-time life. Comprehensively considering the material parameters of the composite pastes and the reliability of the sintered joints under thermal shock, the optimized composite pastes as die attach material in power electronics are obtained. The findings should be inspiring in developing novel die attach materials for high reliable interconnections in SiC power modules.

Effect of chelator on carbon sequestration and mechanical properties of CO2-cured cement pastes with different pore structures

Chelator can accelerate the mineralization reaction of cement-based materials, playing a positive role in reducing CO2 emissions into the atmosphere. Cement pastes with different pore structures were prepared by adjusting the water cement ratio, and effects of chelator on the microstructure, phase composition, carbon sequestration and mechanical properties of CO2-cured cement pastes with different pore structures were investigated in this study. The results indicated that chelator could promote CO2 transport in dense cement paste with more gel pore and transition pore and medium dense cement paste with many transition pore and capillary pore, and induce mineralization reaction to repair larger pores in loose cement paste with more capillary pore and megalopore (LCM). Chelator had the most significant effect on improving the performance of cement paste of LCM, increasing the carbonation sequestration rate and compressive strength of cement paste cured for 48 h by 19.0 % and 28.1 %, respectively.

Comparison of Flexural Strength and Wear of Injectable, Flowable and Paste Composite Resins.

(1) Objectives: This study investigated and compared the wear and flexural strength of two highly filled (injectable), one flowable and one paste composite. (2) Methods: Two highly filled flowable composites (G-aenial Universal Injectable and Beautifil Plus F00), a paste composite (Empress Direct) and a conventional flowable (Tetric EvoFlow) were tested. A two-body wear test was carried out using 10 disc-shaped samples from each group, which were subjected to 200,000 wear machine cycles to simulate wear, followed by Scanning Electron Microscope analysis. Flexural strength was tested using a three-point bend test using 15 beam samples for each of the four groups. Values were statistically compared using one-way analysis of variance (ANOVA) for flexural strength and a Kruskal-Wallis test for wear. (3) Results: The median volume loss for G-aenial Universal Injectable and Beautifil Plus F00 was statistically lower than that of both Empress Direct and Tetric EvoFlow. For flexural strength the two highly filled flowable composites both exhibited statistically higher mean flexural strength values compared to Empress Direct (p < 0.004) and Tetric Evoflow (p < 0.001). There were no statistically significant differences in the values of wear and flexural strength between the two highly filled flowable composites. (4) Conclusions/significance: Highly filled flowable composite resins with nano filler particles outperformed a conventional flowable and a paste composite resin in terms of wear resistance and flexural strength, and may be suitable to use in occlusal, load-bearing areas.

Fabrication of a novel potentiometric sensor based on graphite/carbon nanotube composite paste modified by lead(II)sulfide for efficient determination of copper(II) ions

Fabrication of a novel potentiometric sensor based on graphite/carbon nanotube composite paste modified by lead(II)sulfide for efficient determination of copper(II) ions

Enhancing of hydroquinone and catechol oxidation using a graphite and graphene composite polymer modified paste electrode

ABSTRACT An innovative electrochemical redox response of hydroquinone (HQN) and catechol (CCL) was analysed using a bare graphite and graphene composite paste electrode (BGGCPE) and polymerised L-leucine modified graphite and graphene composite paste electrode (LCN-MGGCPE) was successfully developed in 0.2 M phosphate buffer solution (PBS) with pH 6.0 at a 0.1 V/s scan rate. Fabricated electrode using simple and cost-effective method, the polymerised LCN-MGGCPE surface shows more electrochemical activity, sensitivity and selectivity towards the determination for HQN and CCL. Cyclic voltammetry (CV), linear sweep voltammetry (LSV), Differential pulse voltammetry (DPV), and electrochemical impudence spectroscopy (EIS) were utilised as analytical techniques while LCN-MGGCPE and BGGCPE surface characterisation were studied using a scanning electron microscopy (SEM) technique. LCN-MGGCPE exhibited superior electrochemical activity compared to BGGCPE towards the oxidation responses of both HQN and CCL. Additionally, the effect of pH studies, scan rate change for HQN, and concentration change of analyte molecule were examined, with the 0.025 to 0.500 V/s scan rate varied and revealing an adsorption-controlled process. The concentration changes of CVs methods ranged from 0.2 to 320 μM, DPVs ranged from 0.2 to 1100 μM and LSVs ranged from 0.2 to 850 μM, the calculated a limit of detection (LOD) of CV, DPV, and LSV, is 0.020 μM, 0.026 μM, and 0.011 μM and a limit of quantification (LOQ) of 0.068 μM, 0.088 μM, and 0.035 μM. The electrochemically developed LCN-MGGCPE shows good reproducibility, repeatability, stability, sensitivity and simultaneous analysis of analyte molecules were studied. This study presents a promising pathway for the growth of effective sensors for the determination of HQN in medicinal and water sample applications.

Microstructure characteristics for improved thermal shock reliability of sintered Ag[sbnd]Al paste in SiC power module

To meet the harsh thermal shock (−50–250 °C) requirements of power device packaging, a novel sintered Ag-based die attach material based on the sustained release effect of Al was proposed. In this study, Al particles with natural core-shell structure covered with Al2O3 layer were selected as the ideal doping-phase, and micron Al particles doped sintered Ag composite paste (AgAl) was prepared. First, the microstructural evolution of sintered AgAl joints during thermal shock was studied. The results showed that Al particles effectively suppressed the cracks generation, which attributed to the sustained release effect of Al element. To clarify sustained release mechanism of Al, the interfaces evolution between Ag and Al particles was investigated. In the initial stage, Al was covered by the Al2O3 layer, preventing inter-diffusion between Ag and Al. As the thermal shock proceeds, the Al2O3 film was fractured, achieving direct contact between metal Al and Ag. Diffusion thus takes place. For the sintered Ag5Al joint, the shear strength was 17.3 MPa after 1000 cycles, which is 1.57 times that of pure sintered Ag joint. These results indicate the successful development of low-cost, high-reliability die attachment materials for use in harsh thermal shock environments.

An influence of geothermal water, temperature and pressure on the hydration of multicomponent cement binders

Cement pastes of different compositions were hydrated in a geothermal solution with the simultaneous action of high temperature (150 °C) and pressure (18 MPa) for 7 days. The influence of solution on phase composition and compressive strength of pastes was investigated based on the comparison with hydration in water and using TGA, XRD, FTIR, 29Si, and 27Al NMR. The geothermal solution accelerated hydration and pozzolanic reactions. A higher amount of more thermally stable products was formed. Undesired transformation to crystalline α-C2SH in the samples with the highest C/S ratio was restricted. The uptake of carbonates from the solution led to an increased amount of calcite. As a result, increased compressive strength values were determined. Preferential incorporation of Al3+ into the structure of C-(A-)S-H or hydrogrossular phases depended on the composition of cement pastes.

Blade-Coated Porous 3D Carbon Composite Electrodes Coupled with Multiscale Interfaces for Highly Sensitive All-Paper Pressure Sensors

HighlightsA blade-coated composite paste, composed of a compressible 3D carbon skeleton, PEDOT:PSS, and CNTs, can naturally dry to form a porous electrode on paper with a micro- and nano-structured surface.The all-paper pressure sensor demonstrated an ultrahigh sensitivity of 1014 kPa−1, a wide responsive range up to 300 kPa, and an ultralow operating voltage of 0.01 V.The sensor showcased superior detection capability, ranging from subtle wrist pulses and robust finger taps to large-area spatial force.

Estimation of cement paste stiffness and UHPC elastic modulus through measured phase-property upscaling

The elastic stiffness of bulk concrete materials results from the complex interaction of aggregates, voids, and hydrated cement (which can have multiple hardened phases at multiple length scales). Given the complexities associated with understanding the arrangement of these particles within bulk concrete volumes, estimations for elastic modulus often rely on empirical correlations with unit weight and compressive strength. Such estimations are inherently scale-dependent and fail to capture variability in mix designs, particularly the variability found in specialty concrete mixes. To develop a scale-independent method for estimating elastic modulus from mix-design volume fraction information, this study explores a novel bottom-up approach using cement paste phase stiffness values determined through micro-mechanical experimentation and randomized Monte-Carlo spring arrangement simulations. Statistical representations of cement paste phase stiffness distributions and bulk volume fraction data are combined to provide estimations for elastic stiffness in both the composite cement paste and bulk concrete containing fine aggregate and fibers. Resulting a priori estimations of UHPC cement paste stiffness from the micro-mechanical upscaling simulations were within 4% of measured values (based on mix-design and void volume fraction information alone) for a selected sample of mix proportions. When applied to the two UHPC mixes containing fibers and fine aggregate, upscaling simulations consistently overpredicted the measured elastic modulus, likely due to the aggregate-cement interfacial transition zone (ITZ) properties that were not captured in the micro-mechanical testing.

Impact of Ground Granulated Blast Furnace Slag on Calcium Leaching of Low-Heat Portland Cement Paste.

Low-heat Portland cement and ground granulated blast furnace slag are widely used for the preparation of hydraulic concrete. Nevertheless, the effect and mechanism of corrosion on low-heat Portland cement paste mixed with ground granulated blast furnace slag need to be further explored. This paper investigated the impact of ground granulated blast furnace slag on the calcium leaching of low-heat Portland cement paste by evaluating its mass loss, porosity, leaching depth, compressive strength, and Vickers hardness, and comparing it with the leaching performance of ordinary Portland cement paste. Furthermore, the phase composition and morphology of low-heat Portland cement paste containing ground granulated blast furnace slag were analyzed by X-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy. The results indicate that, after 180 days of soaking in ammonium chloride solution, the mass loss rate, growth rate of porosity, leaching depth, and compressive strength loss rate of low-heat Portland cement paste were 8.0%, 43.6%, 9.1 mm, and 27.7%, respectively, while those of ordinary Portland cement paste were 7.4%, 37.8%, 8.4 mm, and 30.1%, indicating that low-heat Portland cement paste is slightly more damaging than ordinary Portland cement. The addition of ground granulated blast furnace slag could significantly improve the leaching resistance of low-heat Portland cement. For instance, after adding 20% ground granulated blast furnace slag, the above test values were 2.4%, 28.5%, 5.6 mm, and 20.8%, respectively. The reason for this is that ground granulated blast furnace slag has the potential to reduce the porosity of low-heat Portland cement paste, and it can also undergo the secondary hydration reaction with its hydration product Ca(OH)2 to enhance the paste structure. Considering the cost performance, the suitable dosage of low-heat Portland cement paste for satisfactory leaching resistance is about 20%.

Development of a highly loaded zirconium carbide paste for material extrusion additive manufacturing

A highly loaded, aqueous-based zirconium carbide (ZrC) paste was developed for ceramic on-demand extrusion (CODE). Commercial ZrC powder was ball milled to reduce the particle size to ∼1 μm. Paste composition was determined by rheological characterization and observation of printing behavior; the final paste consisted of 46–47 vol% ZrC, 43.5 vol% distilled water, 8.1 vol% dispersant, and 1.6 vol% binder. Rheological characterization of the paste showed a yield stress of ∼8 Pa and shear thinning behavior (ΔG′/Δσ* = −55). The paste was printed using a 610 μm nozzle; a test print showed shape fidelity using the developed paste. A pressureless sintering study was performed; a sintering temperature of 2000°C with a 2-hour hold produced samples of 90 % relative density with 3.8 μm grains, which was consistent with literature. The developed paste, in combination with the pressureless densification results, adds a new, ultra-high temperature material to ceramic extrusion additive manufacturing.

Optimization of Awaze paste formulations: The effects of using spices through a mixture design approach

Previous studies have revealed the microbial quality of Awaze paste. However, limited reports describe the effect of individual spices on Awaze paste quality. A mixture design approach was used to determine the appropriate proportions, with 15 experimental points for independent variables including RP (60–90 %), GA (10–30 %), RO (5–20 %), and GI (5–10 %). The techno-functional properties, particle size, antioxidant activity (DDPH radical assay), proximate composition, iron (Fe), zinc (Zn) content, viscosity, hardness, and microbiological quality of Awaze paste were assessed. The prepared Awaze paste showed a range of characteristics, with antioxidant activity (DDPH radical assay) ranging from 11.86 % to 62.5 %, crude protein content from 6.18 % to 16.22 %, crude fat from 5.7 % to 12.6 %, crude fiber from 16.86 % to 29.06 %, total ash content from 6.32 % to 9.94 %, total carbohydrate from 41.79 % to 60.61 %, energy from 264.3 to 329.2 k cal. , iron (Fe) content from 35.59 to 108.82 mg/100g, zinc (Zn) content from 1.72 to 26.93 mg/100g, viscosity from 65.5 to 125.5 cps, hardness from 8.48 to 55.09 g, yeast and mold count from 0.83 to 2.04 log cfu/g, and total bacterial count from 1.53 to 2.61 log cfu/g. Significant differences (p < 0.05) were observed in proximate composition, techno-functional properties, particle size, antioxidant activity, physicochemical properties, and microbiological characteristics among the formulations of Awaze paste. The selected formula showed a statistically significant difference (p < 0.05) compared to the control sample. The formulation containing 74.79 % RP, 10 % GA, 10.2 % RO, and 5.0 % GI was determined to be the optimal formula with a desirability of 0.73, based on the evaluated parameters. This preferred Awaze paste had a porosity of 28.12 %, particle size of 16.49 μm, antioxidant activity of 63.63 %, crude protein content of 17.28 %, iron (Fe) content of 98.06 mg/100g, and zinc (Zn) content of 15.04 mg/100g. Therefore, this optimal blend of ingredients could be used to produce a consumer accepted Awaze paste.

Large variability and 2H-depletion of Middle Miocene to Pleistocene alkenone hydrogen isotopes in the Equatorial Pacific reflect subsurface, low light haptophyte growth

Hydrogen isotope ratios of haptophyte derived long-chain alkenones (δ2HC37:2) have shown to be a useful tool for reconstructing past isotopic compositions of surface seawater (δ2HSSW). The δ2HSSW is related to global ice volume, sea surface salinity and the local hydrological cycle. Here, we present a hydrogen isotope record of alkenones spanning the last 14.5 Ma from IODP site U1338 in the east equatorial Pacific. The alkenone-based reconstructed δ2HSSW is substantially more negative and variable than reconstructed δ2HSSW based on published oxygen isotopes of coccolith carbonates. This suggests that factors other than the isotopic composition of seawater affect the hydrogen isotopic composition of alkenones. The relatively negative and highly variable δ2HC37:2 values are in line with published modern observations on alkenones from suspended particulate matter in the equatorial and north Pacific, with the highest values at relatively high light conditions at the surface and the lowest values at higher water depth and relatively low light conditions. This suggests that the relatively negative and highly variable δ2HC37:2 values in these Middle Miocene to Pleistocene sediments are likely derived from haptophytes growing below the sea surface under variable low light conditions. In regions where the contribution of alkenones from subsurface production, due to high subsurface nutrients, at low light intensities to the sediment is relatively high the δ2HC37:2 has to be interpreted with care as a proxy for δ2HSSW.